Explosions tore through the departure hall of Brussels airport on Tuesday morning killing up to 21 people and injuring 30 others and a second blast struck a metro station in the capital shortly afterwards, the Belgian public broadcaster RTBF said.

The Belga agency said shots were fired and there were shouts in Arabic shortly before the blasts at the airport. Pictures on social media showed smoke rising from the terminal building through shattered windows and passengers running away down a slipway, some still hauling their bags.

The blasts at the airport and metro station 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.

Airport spokeswoman Anke Fransen said: “There were two blasts in the departure hall. First aid team are in place for help.”

Brussels airport said it had cancelled all flights and the complex had been evacuated and trains to the airport had been stopped. Passengers were taken to coaches from the terminal that would remove them to a secure area.

Police did not give any confirmation of the cause of the blast. But there has been a high state of alert across western Europe for fear of militant attacks backed by Islamic State, which claimed responsibility for the Paris attack.