Video report by ITV News Correspondent Damon Green
Detective are questioning four men held after a Tuesday operation to stop a suspected Christmas terror plot.
The arrests were made in a series of coordinated raids in South Yorkshire and Derbyshire and the Army's Bomb Disposal Unit was dispatched to an address in Chesterfield and was later sent to a community centre and mosque in Sheffield.
The immediate area around the Chesterfield property was cordoned off and residents evacuated as officers carried out searches on Tuesday. The cordon has since been reduced but the property remains sealed off.
A 31-year old man was arrested from the home in Chesterfield, while three others, aged 22, 36 and 41, were detained at different addresses in Sheffield.
All four were arrested on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism under Section 41 of the Terrorism Act 2000.
Intelligence sources have told ITV News that the timing of the raids was "significant and a suspected plot was imminent".
The raids come as extra security is in at festive events, such as at Christmas markets, with the threat of an attack at this time of year is anticipated by anti-terror officers.
The suspects held on Tuesday are being questioned at a police station in West Yorkshire.
Police said the arrests were "intelligence-led and pre-planned" as part of an ongoing investigation by the North East Counter Terrorism Unit.
A total of four properties are being searched in connection with the probe - four in Sheffield and one in Chesterfield.
One of the buildings being searched in Sheffield is the Fatima Community Centre in the Burngreave area in the north of the city.
The Army's Bomb Disposal Unit was sent to the community centre after completing its work in Chesterfield.
A resident living near to the Fatima Community Centre said he was woken by three bangs in quick succession, and believed one of them came from the community centre but the others appeared to come from nearby flats.
One of the flats is understood to have been raided.
The main door to the community centre also appeared to be on the floor in pieces.
In the Meersbrook area of Sheffield, residents said they were woken by police blowing open the door of a run-down terraced house as their street was swamped by heavily armed officers in protective gear.
Only the searches in the Burngreave area of Sheffield, and in Chesterfield, will resume on Wednesday morning, the others have concluded.
A police statement said: "The Army's Bomb Disposal Unit attended an address in Chesterfield.
"As a precautionary measure and in the interest of public safety, the immediate area was cordoned off and local residents evacuated while a thorough search was carried out.
"We recognise that local people may have concerns as a result of this activity. We would ask people to remain alert but not alarmed and we are grateful for the assistance and understanding of people locally."
Police added that loud bangs heard at the time officers entered the premises were part of the method used to gain access.
People living near an address in the Meersbrook area of Sheffield said they were woken at around 5.30am.
Retired Joan Miller, 63, who lives opposite the run-down house, said: "It was a very loud bang. It shook the house. I pulled the curtains and saw lots of armed men in the street, so I kept watching because that was quite extraordinary."
Tuesday's arrests came as police and MI5 tackle a terror threat that is seen as unprecedented.
In addition to five attacks that took place in London and Manchester, Home Secretary Amber Rudd revealed earlier this month that security agencies have foiled nine plots since the Westminster atrocity in March.
Counter-terror teams are running about 500 live investigations involving 3,000 individuals at any one time, while there is also a wider pool of 20,000 subjects of previous probes.