'Blood flooding the floors': Witnesses recall chaos as terrorists attack Belgium

Two explosions at Belgium's airport shattered glass and blew out wall panels in deadly blasts that killed a dozen travellers, setting off a wave of terror across the city.

Victims ran for their lives through dust and debris as pillars of smoke rose from the terminal through its shattered glass roof.

One witness described a scene of utter chaos and violence with "blood flooding the floors" as survivors tried to hold their wits together and escape.

"Everywhere there were bodies with no head," Yassine Amrani told Politco.

"There was a woman screaming while she was holding her baby and screamed, 'where is my baby?'"

The 39-year-old tried to help the woman, saying: "I told her she was holding child but she said she had one other that she couldn't find."

Belgian David Crunelle was headed to Japan when the bombs went off near the American Airlines departure longue.

"An explosion happened in the terminal for the US departures. I think it was American Airlines terminal. Two explosions, (with) like two or three seconds between the two explosions. Everything went dark," the 36 year old told the ABC.

"There was a lot of people injured. Instantly, everybody, they started screaming and crying a lot, exiting — the people from the airport and from the airline companies — everybody went out without knowing what to do but it went well."

Expressions of grief and support are flowing for the people of Brussels as its people and the world come to grips with the co-ordinated terror attack in European capital.

Major European cities are ramping up security while Belgium goes into its highest state of alert in fear and vigilance in the face of more possible attacks.

Belgian authorities have confirmed they are treating the two bombings at the Brussels Airport and a subsequent bombing at the city's Metro system as suicide attacks.

The attacks have so far left more than 30 dead and close to 200 injured.

France has deployed 1,600 troops around railway stations, airports and border points with a further 400 troops deployed in Paris.

British police are following suit as the nation's top counter-terror officer, Mark Rowley, says the ramp-up is precautionary and not a result of a specific threat.

"In London specifically, the Metropolitan Police Service has mobilised additional officers, who will carry out highly visible patrols at key locations around the capital including the transport network," Rowley said in a statement.

With police and military forces are stepping up around the continent, European leaders have expressed their sorrow and disbelief over the terror attack.

A White House spokesperson told Yahoo President Obama was apprised this morning of the explosions in Brussels, adding US officials have been and will continue to be in close contact with their Belgian counterparts, and we will provide additional information and updates as we are able to do so.

Australian Prime Minister Malcolm Turnbull.

British Prime Minister David Cameron.

President of Lithuania Dalia Grybauskait.

Lithuanian Prime Minister Algirdas Butkevičius.

European Commissioner for Transport Violeta Bulc.