BRUSSELS: At least 10 people were killed and 30 wounded in explosions at Brussels Zaventem airport on Tuesday morning, Belgian broadcaster RTBF cited a hospital source as saying.

A blast was later heard at Maelbeek metro station in Brussels, close to the EU institutions, RTBF said.

Brussels transport authority said all metro stations in Brussels are closing.

—AFP

The Belgium broadcaster VRT said the Brussels airport explosion was a suicide attack, Reuters reported. This is unconfirmed at this stage.

Images on the RTBF website showed smoke rising from the terminal building, where the windows had been shattered. RTBF said the airport had closed followed the explosions.

Shots were fired and words in Arabic shouted before the blasts occured, Belgian media reported.

Belgian media said rail traffic to the airport was suspended. Brussels Airport serves over 23 million passengers a year.

Television footage showing panicked people fleeing the airport premises following the blasts.

Sky News in London said the blasts had occurred in the departures lounge and cited reports it had occurred near the American Airlines desk.

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.”

Brussels Airport is cancelling flights and evacuating the airport area, it said on its Twitter account following two explosions at the airport on Tuesday morning.

Brussels airport is closed until further notice, Eurocontrol, the European organisation for air navigation safety confirmed on its website Tuesday following twin explosions.

'Highest terror threat'

Belgium has raised terror threat across the country to the highest level, the country's interior minister said.

The blasts occurred four days after the arrest in Brussels of Salah Abdeslam, a suspected participant in November militant attacks in Paris that killed 130 people.

Belgium's Interior Minister, Jan Jambon, said on Monday the country was on high alert for a possible revenge attack following the capture of 26-year-old Abdeslam.

“We know that stopping one cell can ... push others into action. We are aware of it in this case,” he told public radio.

French investigator Francois Molins told a news conference in Paris on Saturday that Abdeslam, a French citizen born and raised in Brussels, admitted to investigators he had wanted to blow himself up along with others at the Stade de France on the night of the attack claimed by the militant Islamic State (IS); but he later backed out.

Belgian police had been on alert for any reprisal action.

This is a developing story and will be updated accordingly.