Belgian state broadcaster said the Tuesday blasts had left several dead and many injured. National security level was raised to its maximum.
Belgian broadcaster VRT said at least 13 people were killed and 35 severely injured after the explosions.
Another explosion was reported at Brussels Metro Station close to EU institutions, Belgian broadcaster RTBF said.
Some 10 people were killed the in metro station blast, local television channel VTM reported.
Several people were also injured in the explosion at Maelbeeck metro station.
"Some 10 people were killed the in metro station blast, local television channel VTM reported."
Brussels Metro operator STIB announced on Twitter that the metro is closing.
Belgium's rail operator says the main train stations in Brussels have also been shut down.
Brussels University and museums were also evacuated in the wake of the blasts.
Furthermore, all Brussels-bound flights, including several by British Airways and Turkish Airlines, have been rerouted.
Jaume Duch, the European Parliament's press representative, told French daily Le Monde that security is being stepped at the parliament building in Brussels.
In the airport, shots were fired prior to the explosions, the Belgian news agency has reported.
Hundreds of people were evacuated onto the tarmac at theZaventem Airport following the explosions.
"In the airport, shots were fired prior to the explosions, the Belgian news agency has reported."
Three explosives vests were reportedly found in Brussels airport.
Belgian PM Charles Michel said he is following the situation "minute by minute," adding that the victims are his "absolute priority."
Airport spokeswoman Anke Fransen said: "There were two blasts in the departure hall. First aid team are in place for help."
The blasts are believed to have occurred at the American Airlines check-in desk at around 8 am local time (0700 GMT).
Footage released on social media showed people running away with smoke billowing from the building. Windows were also shattered due to the shockwave.
An MP whose wife was present at the airport said that the wounded were hit by glass ceiling tiles.
"The blasts are believed to have occurred at the American Airlines check-in desk at around 8 am local time (0700 GMT)."
The explosions came four days after the apprehension in Brussels of Salah Abdeslam, the main suspect behind the November Paris attacks that killed at least 130 people.
Belgian media said the airport was being evacuated and no flights were allowed. Rail transport to the facility was also halted. The Brussels airport serves 23 million passengers annually.
London and Paris officials are reinforcing security at key hubs following the attacks.
UK Foreign Secretary Philip Hammond said the London government was in touch with the Belgian authorities and the situation was "ongoing."
British Prime Minister David Cameron said he has called a meeting of the UK government’s emergency committee, COBRA, in the wake of the Brussels attacks.
French President François Hollande is holding an emergency meeting with senior cabinet members. The blasts in Brussels come days after the arrest in Brussels of the top suspect in the November 13 Paris attacks, Salah Abdeslam.
Security was also reinforced at Frankfurt Airport in Germany, police said.
Meanwhile, Dutch counter-terrorism officials said they are tightening security at national airports and controls on the southern border with Belgium. Extra police patrols at Schipol, Rotterdam and Eindhoven and border controls on the southern border, Press TV reported.
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