Authorities said two "walking wounded" were also taken to hospital after the blast at Haut du Mont on Pier Road, St Helier early yesterday morning.
Officers said relatives are being contacted and the fire has now been extinguished.
Timeline of events:
The Jersey Fire Service attended the block of flats on Friday night after reports of the smell of gas were reported.
Speaking at a press conference on Saturday, Robin Smith, the chief officer at States of Jersey Police, said the fire service had been called after residents reported smelling gas.
Around 4am on Saturday
Police received reports of a "large explosion" at the block of flats.
Emergency services are dispatched to the scene.
Nearby residents reported hearing a massive bang around 3.50am.
CCTV footage obtained by ITV News showing the moment of the tragic explosion in St Helier
Daniel Hunt, a 19-year-old data administrator, who lives across the bay, said the explosion woke him at around 4am.
“My bedroom was shaken from the explosion with the windows rattling, which was all very unnerving,” he said.
“I went outside to take a look…I could see what looked like police and firefighters shining torches through windows of surrounding buildings.
"I assume as they were evacuating the surrounding area.
“The building (was) up in flames with smoke pouring out of the windows.
“To have this happen so close and so early in the morning you don’t know what to think.”
9am on Saturday
The Parish of St Helier confirms the Town Hall is hosting those impacted by the explosion.
A tweet reads: "The Town Hall is currently hosting those affected by this morning’s incident. We ask that you respect the people who are here.
"At the moment donations and additional support from the public aren’t needed. We will update you as the situation changes."
Haut du Mont on Pier Road before the explosion
10am on Saturday
First UK crew arrives to assist efforts.
12pm on Saturday
Police confirm at least one person has died and "around a dozen" are still missing after the explosion.
Two "walking wounded" have been taken to hospital as police on the Channel island search the site.
Officers confirmed relatives are being contacted and "significant work" is being carried out at the scene.
12.15pm Jersey Police press conference
Robin Smith, chief officer at States of Jersey Police, said reports of the blast came in at around 4am this morning.
He described the scene as "devastating" adding more fatalities are possible.
Mr Smith said: "We have a three-storey building that has completely collapsed - described from a demolition point of view as a pancake that has dropped almost straight down.
"There is also damage to a nearby building as well, another block of flats that the fire service needs to make safe.
"It is a pretty devastating scene, I regret to say."
When asked about the likelihood of further deaths, Mr Smith said: "I wouldn't want to speculate on those sorts of things...but there has to be a recognition that we could have more fatalities."
12.30pm on Saturday
Jersey residents have been urged to avoid using the A&E department on the island unless it is an emergency.
Police also told people to avoid Haut du Mont on Pier Road, St Helier.
12.45pm on Saturday
Kristina Moore, the chief minister of Jersey, said the flats were run by Andium Homes, who were working to ensure anyone who has been displaced has somewhere to stay on Saturday night.
The state-owned but independent company which rents out thousands of properties on the island, said on Twitter: "We are working with the emergency services responding to the incident at Haut du Mont this morning.
"Our focus at the moment is on supporting our residents on that estate. Our thoughts are with them and their families at this time."
3.30pm on Saturday
The Government of Jersey said the Town Church in St Helier would be open until 8pm on Saturday for anyone affected by the explosion.
A statement on Twitter said: “The Town Church is open until 8pm this evening and has set up a space for Islanders who wish to light candles for all who have been affected by this incident.
"The church has also set up a space with tea and coffee for Islanders who simply need a place to process recent events.”
On Saturday afternoon, Jersey Police confirmed "pockets of fire have been discovered" still burning beneath the rubble as the search continues at the Haut du Mont flats on Pier Road.
4.30pm on Saturday
Deputy Prime Minister Dominic Raab said he is "deeply saddened" after the explosion at the three-storey block of flats.
He tweeted: "I’m deeply saddened by the incident in Jersey this morning and my thoughts are with everyone affected.
"I commend the work of the emergency services responding and we stand ready to support in any way we can."
4.45pm Jersey press conference on Saturday
Another press conference takes place to inform the public about progress with the rescue efforts.
Mr Smith said: “A number of staff have worked very long days.
"This is a protracted incident and this is going to go on for days, maybe weeks, and therefore it is important to have resources to continue to keep going.”
Jersey's Chief Minister, Kristina Moore, praises the hard work of the rescue teams combing through the wreckage at Haut du Mont
At the press conference, the death toll for the tragedy was confirmed to have risen to three.
Specialist teams are now looking for six more.
The final total is estimated to be up to a dozen, as details on visitors to the flats are unknown.
Specialist teams from the UK's Ministry of Defence and fire services have been supporting local crews.
They include the South West Hazardous Area Response Team, alongside an Urban Search and Rescue Team from Hampshire & Isle of Wight Fire & Rescue Service.
Jersey Fire and Rescue Service’s chief fire officer, Paul Brown, told a press conference on Saturday that their primary challenge is navigating the “dangerous structure”.
Mr Brown also confirmed that firefighters had been called to the building at 8.36pm on Friday and had carried out investigations after residents reported smelling gas – just hours before the blast.
Chief Minister Kristina Moore said at least three people had been killed, describing the incident as an “unimaginable tragedy” for the Channel Island.
5pm on Saturday
Another UK crew arrives to assist in rescue efforts. Urban search and rescue teams, including search dogs, arrive.
7pm on Saturday
Extra specialist equipment from military aid including a military helicopter arrives.
Around 20 off-island rescue specialists arrive and 10 Jersey firefighters continue efforts at the tragedy.
Footage of the military helicopter arriving to assist the rescue efforts
Overnight on Saturday
Emergency services continued to work through the night after the explosion looking for more survivors.
Jersey's government tweets a video of firefighters and specialist rescue teams on the scene.
The footage revealed some of the devastation and debris left behind after the blast, including crushed cars and a blown-out window.
8am on Sunday
The search and rescue operation for around a dozen missing people after an explosion at a block of flats in Jersey has become a recovery operation.
Jersey's Chief of Police, Robin Smith, said: "It is with sadness that I am confirming that the search and rescue operation had been moved to a recovery operation.
"The decision was made after a detailed assessment and following the use of specialist K9 units.
“Disaster Victim Identification (DVI) strategies are in place and specialist officers are surveying the scene with Fire and Ambulance Services and tactical advisors from Urban Search and Rescue (USAR).”
11.45am press conference on Sunday
Chief of Jersey Police Robin Smith told the press conference that the families of the victims were being supported.
He said: “We have moved to a recovery stage, it’s a moment to think about the families.
“We have deployed family liaison officers to the families, it’s utterly important we are sensitive to their emotions as we begin a meticulous and painstaking search of the debris following the explosion.”
He added: “We are not going to be here for days, we are going to be here for weeks and it’s important I make that clear.”
He added: “It is not going to happen quickly, it’s going to happen carefully and sensitively.”
Mr Smith said 12 people are still missing, adding the situation must be handled sensitively and precisely.
He said: "This is a very sensitive area and it’s very difficult to be precise.
“The area I can be precise on is we have three confirmed fatalities and it’s fair to say we expect to find more.
“Previously we have said in the region of a dozen but it’s difficult to make that assessment. That’s the number we hope we do not get to but that is the number we are working to.”
He also revealed it "looks likely" the blast was the result of a gas explosion, but currently they "do not know".
Paul Brown, Jersey chief fire officer, acknowledged that something has gone “horribly wrong” after the fatal explosion.
Speaking at this morning's press conference, he said: “Something clearly has gone wrong as a building has exploded and collapsed.”
He added that it had gone “horribly wrong”.
Mr Brown told reporters that the fire service will be “co-operating fully” with “honesty” and “transparency”, but the main focus is currently the search operation.
Chief Minister Kristina Moore told the press conference: “The wider community of Jersey has been immensely shocked and saddened at the events of this week but people simply wanted to step up and support members of the community.
"We have offers of support from all sides of the community because we are all touched by these events and sheer compassion for our fellow islanders, and want to support them.
"We are overwhelmed and want to channel these efforts as best we can.”
The island's emergency helpline - set up during the coronavirus pandemic to report symptoms - has been turned into a support line for friends and family looking for information about family members caught up in the incident.
It can be reached on 0800 735 5566.
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