BRUSSELS, March 22- The blasts occurred four days after the arrest in Brussels of a suspected participant in November militant attacks in Paris that killed 130 people. Belgian police had been on alert for any reprisal action.
As many as 13 people were killed in the explosions and another 35 were severely injured, Belgian broadcaster VRT said.
Social media showed pictures of smoke rising from the departure hall where all windows had been shattered by the blast. Passengers were seen running away down a slipway from the departure lounge.
Sky News television's Alex Rossi, at the scene, said he heard two "very, very loud explosions".
"I could feel the building move. There was also dust and smoke as well...I went towards where the explosion came from and there were people coming out looking very dazed and shocked."
"The thinking here is that it is some kind of terrorist attack - that hasn't been verified by any of the authorities here at the airport."
Belgian media said rail traffic to the airport was suspended.
There was no immediate official comment on the cause of the attack.