A manhunt has been launched for one of the terrorists behind coordinated bombings in Brussels which left 34 dead and almost 200 injured.

As a series of police raids were mounted across Belgium, prosecutor Frederic Van Leeuw said two suicide bombers died in the attack on the main airport in Brussels and a third was being "actively" sought.

Belgian police issued an image of the man, one of three seen pushing luggage trolleys through Zaventem airport moments before two bombs exploded.

The Herald:

A third bomb was deactivated at the airport hours after the attack.

In a statement, Belgian police appealed for information about the man, who is wearing a hat and a light-coloured jacket.

Read more: UK flights to Brussels cancelled for second day

"Police are looking to identify this man. He is suspected of having committed the attack at Zaventem on Tuesday March 22," it said.

"If you recognise this individual or have information regarding this attack please call 0800 30 300."

The airport attack was followed by a bomb blast on a Metro train in the city centre as terrorists inflicted a new outrage on a European capital.

Mr Van Leeuw said: "A photo of three suspects was taken at Brussels airport.

"Two of them have probably committed a suicide attack, the third - dressed in a white jacket and wearing a hat - is actively sought."

The prosecutor added: "Various departments and experts are currently in various crime scenes. This will take place for many hours to come.

"Due to the violence of the attacks, this investigation is particularly difficult.

"Various operations are ongoing across the country and several witnesses have been heard.

"Federal magistrates supported by magistrates from our organisation are present in various strategic and operational points as well as in the government's crisis centres in order to coordinate operations.

"Several explosions have been heard. They are due to bomb squad activity upon the discovery that the suspects might have left explosives behind. And this could continue."

The attacks left a major city in lockdown once again less than five months after Paris was hit by a wave of deadly strikes.

The atrocities on Tuesday, condemned as "blind, violent and cowardly" by Belgian Prime Minister Charles Michel, came after the arrest last week of terror mastermind Salah Abdeslam, who plotted November's massacre in the French capital.

The terror group Islamic State (IS) has claimed responsibility for the Brussels attacks.

Security was being stepped up at major transport hubs around the continent, with British police forces boosting numbers at "key locations" including ports, airports and the rail network.

French Prime Minister Manuel Valls said: "We are at war. In Europe we have been subjected to acts of war for several months."

As the city went into lockdown:

:: Local media reported that 20 people were killed following the blast at Maelbeek metro station, while 14 died in the suicide attack at the airport

:: The number of people injured in both attacks was believed to be 198

:: Two Kalashnikov rifles and an unexploded bomb belt were found at the airport

:: Downing Street said one British national is known to have been injured

First news of the attacks came when the airport was rocked by a double blast around 7am UK time. It was blamed on suicide bombers.

The attack on the Metro came about an hour later.

Jef Versele, 40, from Ghent, told the Press Association: "I was on my way to check in and two bombs went off - two explosions.

"I didn't see anything. Everything was coming down. Glassware. It was chaos. It was unbelievable. It was the worst thing."

Footage from inside the airport building showed a scene of devastation with ceiling tiles strewn across the floor and suitcases abandoned.

Images of passengers climbing from a train into a smoke-filled tunnel near Maelbeek station were reminiscent of scenes following the July 7 attacks in London.

Other images showed the injured from the Metro being treated in the street, while at the airport people could be seen fleeing in terror in video footage shot from an airport car park.

As the army was deployed and the transport system was locked down, Mr Michel said: "In this tragic and dark moment for our country, more than ever I call everyone to show calm but also solidarity."

International leaders united in support for Belgium, with David Cameron branding the atrocities "appalling" and US president Barack Obama condemning the "outrageous attacks against innocent people".

The Prime Minister's official spokeswoman said Britain was also sending a team of specialist police officers to the city to assist with the investigation.

And the Foreign Office updated its travel advice to Belgium, advising against travel to Brussels.

Mr Michel said the atrocities had killed people whose lives "were in full course".

He said: "The lives of people who were most likely travelling without a care in the world, going to work or to school, lives that have been broken by extremism."

One eyewitness, Theo Vassilopoulos, said Maelbeek station remained completely closed off on Tuesday evening with police cars and officers still in the area.

The 36-year-old from Greece, who has lived in Brussels for seven years, described chaotic scenes as people poured out of the station following a bomb blast.

Mr Vassilopoulos, who works at the European Parliament with the Greek MEP Stelios Kouloglou, told the Press Association: "It all started with a distant sound, we didn't realise what it was.

"But a few moments later we heard people shouting and screaming so we went by the window and we saw lots of people coming out of the station. I saw some of them had serious injuries, head injuries, a lot of blood on their head, wounds on their legs.

"We realised something was going on. More people kept coming from inside the station and some of them were in dusty clothes or their clothes were torn apart, so then we knew that there was an explosion or something bad."