A police woman gestures in front of ambulances at the scene of a blast outside a metro station in Brussels, in this still image taken from video on March 22, 2016. [Photo/Agencies] More photos

European governments moved swiftly to beef up security in the wake of the attacks in Brussels which officials say killed many people and injured over one hundred people.

In London Prime Minister David Cameron chaired a meeting of COBRA, the government committee which coordinates security in the UK. It groups senior cabinet ministers, intelligence chiefs, senior police officers and military officers, including those from the elite SAS regiment.

Similar meetings were taking place in Paris, Berlin and other key European capitals, and officials said extra security was being put in place at airports and travel hubs throughout the continent.

In France, President Francois Hollande ordered an extra 1,600 police and paramilitary officers onto the streets of Paris. Security and police checks were also established at borders throughout the Schengen area of mainland western Europe, normally open to free travel between countries, officials said.

In Germany extra security was drafted in to cover key public areas as well as airports and railway stations, according to local media.

The British Broadcasting Corporation put the death toll at 31, of which?11 were killed at Zaventem Airport and?20 dead at Maelbeek metro station, near the area where many EU offices are located.

Hollande told reporters "This is a war against terrorists. France has moved to consolidate our borders. It will be a long war, but we should be calm and determined.

"Today we are with Belgium. It was Europe that was targeted, and we should be united," he added.

London mayor Boris Johnson said "We are stepping up the security presence at major security hubs. This is partly for security and partly for reassurance purposes."

Police in the British capital patrolled rail stations and airports armed with semi-automatic weapons, a rare sight in a country where the police are not routinely armed. Dogs trained in sniffing explosives were also deployed, security officials said.

Long queues formed at London"s airports, in part because of increased security checks on passengers, and in part because of delayed and cancelled flights. Brussels airport, scene of two bomb blasts, was closed, and the flight situation in Europe was compounded by a strike involving French air traffic controllers, UK television channels reported.

In Belgium armed soldiers patrolled the streets as the security threat was raised to the highest level. Belgian Prime Minister Charles Michel cancelled a planned trip to China because of the situation.

Michel said he was sending up to 200 extra troops to the capital to join those already deployed, and added: "What we feared has happened. It is a black moment in our country. We should face up to this challenge by being united, and coming together."

In the UK the threat level from international terror attacks was severe, which means an attack is considered likely.

UK security officials who requested anonymity said intelligence monitoring was being shared with other security services in Europe, including so-called "chatter" on mobile devices and social media which often immediately precede an attack.

Governments throughout Europe had been on alert since gun and bomb attacks in Paris on November 13 killed 130 people and wounded hundreds of others. The suspects, many of whom died in the attacks, were traced to the Molenbeek area of Brussels, home to many migrants.

The main suspect, Salah Abdelslam, was arrested by Belgian police and special forces troops after a gun battle in Molenbeek four days ago. Government officials throughout Europe have said they feared an attack as a result of Abdelslam"s arrest, which was hailed as a breakthrough by intelligence chiefs.

French media reports said officials were sifting through the debris from today"s Brussels attacks for evidence of suicide vests, which they hoped may offer DNA and other traces to link them with the abandoned vest found after the Paris attacks in November.

To contact the reporter: [email protected]