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.
Some reports from the scene speak of casualties but 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.