Several explosions have struck Brussels airport and the metro system, causing at least 34 deaths, Belgian media say.
Two blasts tore through the departures area of Zaventem airport shortly after 08:00 local time (07:00 GMT).
An hour later, an explosion hit Maelbeek metro station, close to the EU institutions. The airport and whole transport system have been closed.
The attacks come four days after Salah Abdeslam, the main fugitive in the Paris attacks, was seized in Brussels.
The Belgian government has yet to confirm the number of deaths and injuries or the cause of the explosions.
Belgium has now raised its terror threat to its highest level.
Prime Minister Charles Michel tweeted: “For the moment, we are asking people to stay where they are.”