Brussels has been targeted in a series of deadly terrorist attacks.

Explosions ripped through the city's international airport and metro system during rush-hour on Tuesday morning, leaving at least 34 people dead and many others seriously injured.

The coordinated attack - apparently carried out by so-called Islamic State - comes days after the arrest of Salah Abdeslam, who helped plot November's Paris attacks, in a suburb of Brussels.

Security has been stepped up across Europe amid fears further attacks may be launched.

Here's what we know about the latest terrorist atrocity to hit the continent.

  • Where were the explosions?

Zaventem Airport

The attack was launched at around 8am. Credit: ITV News

Zaventem Airport was rocked by a twin bomb blast at around 8am local time (7am GMT).

Witnesses said shots were fired and shouts in Arabic were heard before two explosions tore through the busy departure lounge.

The first blast happened near the excess baggage desk, with the second hitting a nearby Starbucks cafe.

Footage showed scenes of devastation and chaos inside the terminal.

Pictures posted on Twitter showed people running from the airport with smoke billowing from the building.

People fleeing from Brussels airport. Credit: Reuters

Two Kalashnikov rifles and an unexploded bomb belt were found at the airport after the attacks.

The attackers are believed to have hidden their bombs in their luggage.

Metro system

The metro is situated close to the EU headquarters. Credit: ITV News

Maelbeek Metro Station - which lies close to the headquarters of the European Union - was struck around an hour later.

Image showing the aftermath of the Metro bombing. Credit: Alexandre De Meeter/Twitter

The bomb was reportedly detonated in the middle carriage of a train which was running along the platform at the time.

In scenes reminiscent of the 7/7 bombings in London, passengers were seen climbing from trains into a smoke-filled tunnel.

Near the entrance to the station, rescue workers set up a makeshift medical camp in a pub.

Shocked morning commuters streamed from the entrances as police set up a security cordon.

Emergency personnel are seen at the scene of the metro station blast. Credit: Reuters
  • How many people have been killed?

At least 34 people have been killed, according to latest reports.

The fatalities include:

14

at the airport

20

at the metro station

An estimated 170 people have been injured in both attacks with many sustaining serious leg injuries.

Two British nationals are among the wounded, the Foreign Office has confirmed to ITV News.

  • Who carried out the attacks?

The three suspected bombers entering the terminal.

So-called Islamic State claimed responsibility for the attacks.

In a message released via a news agency linked to the group, IS said the series of bombings involved "explosive belts and devices".

A CCTV image showing three men suspected of carrying out the airport attacks also emerged.

Two men in black - wearing a single glove to apparently hide a detonator - are thought to have blown themselves up during the attack.

One of the men has been named as Ibrahim El-Bakraoui who was known to police prior to the deadly attacks.

Turkish authorities said on Wednesday that they had arrested Ibrahim El Bakraoui and deported him to the Netherlands last year.

Ibrahim's brother Khalid has also been named as the attacker who targeted the city's metro in a coordinated attack and was also reportedly known to police.

According to reports, Khalid had rented a flat in the Belgian capital, under a false name, which was raided last week and where an Islamic State flag, an assault rifle, detonators and a fingerprint of the Paris attacks prime suspect were found.

L-R: Suicide bomber brothers Khalid El Bakraoui, who bombed the metro station, and Ibrahim El Bakraoui, who bombed the airport (pictured centre in CCTV) Credit: Reuters/AFP

The other man in black who died in the airport picture has been identified as 25-year-old Paris bomb-maker Najim Laachraoui.

A third man pictured at the airport, dressed in white and wearing a hat, is believed to have fled the scene after his bomb failed to go off.

An international manhunt is now under way to capture him.

A manhunt is underway for Najim Laachraoui

The taxi driver

A taxi driver revealed how he took the brothers and Laachraoui to the airport and said that the men had initially wanted to take five pieces of luggage with them, but he only had room for three.

Unknown to the driver at the time, the luggage was packed with explosives.

  • Why has Belgium been attacked?

Salah Abdeslam. Credit: Police handout

The bombings are likely to be in response to the arrest of Salah Abdeslam near Brussels last week.

Prosecutors believe Abdeslam, a Belgian-born French national, was heavily involved in November's Paris attacks which left 130 people dead.

Belgium's Interior Minister, Jan Jambon, said on Monday the country was on high alert for a revenge attack.

  • Brussels on lockdown

Armed police outside the metro station after the blast. Credit: Reuters

All public transport in Brussels was stopped and the government raised the country's terror threat to the highest possible level.

The airport cancelled all flights and train services on the cross-channel tunnel from London to Brussels were also suspended.

Extra troops were sent into the city and the authorities urged citizens to stay in their homes or offices and not to use the already strained telephone networks.

Restrictions were relaxed by late afternoon and parts of the public transport network were back in operation.

  • What have eyewitnesses said?

Injured people are seen at the scene. Credit: Reuters

Jef Versele, 40, was on his way to check in when the first explosion went off.

Everything was coming down. Glassware. It was chaos. It was unbelievable. It was the worst thing.

Jef Versele

Alphonse Youla, who works at the airport, said he heard a man shouting in Arabic before the attacks.

Then the glass ceiling of the airport collapsed.

Alphonse Youla

Sky News journalist Alex Rossi was at the airport when he heard two "very, very loud explosions".

I could feel the building move.

Alex Rossi
  • How have world leaders reacted?

Belgium Prime Minister Charles Michel called the attacks "blind, violent and cowardly", saying they were a "tragic moment in our country's history".

"What we feared has happened," he said.

Charles Michel addressing reporters.

David Cameron, who chaired an emergency Cobra meeting following the attacks, said Europe must stand together to ensure "these appalling terrorists" can never win.

French President Francois Hollande called it an "attack on Europe" and said the whole continent was "at war" with terrorists.

French President Francois Hollande and Prime Minister Valls. Credit: Reuters

President Barack Obama sent a message of support to the people of Brussels, saying: "We can and we will defeat those who threaten the safety and security of people all around the world."

EU Foreign Policy Chief Frederica Mogherini fought back tears as she reacted to the news.

"Today is a difficult day," she said.

Pope Francis also condemned the "blind violence" of the attacks and offered prayers for the victims, their families and emergency responders.

Pope Francis. Credit: Reuters
  • Security stepped up across Europe

Armed police officers on patrol at St Pancras in London. Credit: Reuters

Countries across Europe quickly announced extra security measures in response to the bloodshed.

Police numbers were stepped up at key locations around the UK in what the country's most senior counter-terrorism officer said was a precautionary move.

The French interior minister also announced that an extra 1,600 police officers had been deployed to stations, airports and border crossings.

UK police also called on any Britons who were in Brussels and have pictures or video of the attacks to upload the material to a special website so it can be passed on to investigators.

False report of an arrest

On Wednesday local media reported that the manhunt for Laachraoui was over and he had been arrested in the Anderlecht district of the city but new information suggests the man "was misidentified".