Two explosions have been reported at Zaventem airport in Brussels.Images on social media from the scene showed smoke rising from one of the terminal buildings. The cause of the explosions is unknown.
Reports say the blasts were in the departures area and speak of casualties although this has not been confirmed.
The blasts come four days after the capture in Brussels of Salah Abdeslam, the main suspect in the Paris attacks in November.
Belgian media say the airport is being evacuated. It has been closed to flights. Rail transport to the facility has been halted.
Social media reports from the scene speak of panic as people fled the airport buildings.
Images showed a swathe of shattered glass on one of the buildings.
Other reports say at least one explosion was close to the American Airlines check-in area but again this has not been confirmed.
The Belgian broadcaster RTBF quoted a witness as saying there were people injured or unconscious in the departure area, opposite the Sheraton hotel.
Niels Caignau, a Swissport employee, told Flemish broadcaster VRT: "I was on a break and heard and felt a big explosion - we have from here a view over the departure hall and saw a plume of smoke come out.
"The windows are completely shattered. People went outside in shock. It doesn't look good."