At least 34 people have been killed and nearly 200 wounded after apparently co-ordinated attacks at Zaventum Airport in Brussels and a metro station elsewhere in the city.
Shots were fired as the attackers reportedly shouted in Arabic before two explosions at the airport.
Maalbeek metro station was targeted in a separate attack during the morning rush hour.
An empty pushchair could be seen surrounded by debris from an explosion at the airport, while children could be heard screaming after the underground blast.
At least 14 people died and 96 were wounded in the twin blasts, and some 20 people were killed and 106 injured – 10 critically – in the metro explosion.
Marc Decramer, a spokesman for University Hospital Gasthuisberg in Leuven, east of Brussels, told Flemish language broadcaster VTM that some of the wounded had suffered fractures and deep cuts caused by flying glass and nails.
Belgium’s federal prosecutor said all three explosions were “terrorist attacks”.
“There were two explosions in the departure area, one probably caused by a suicide bomber,” said Frederic Van Leeuw of the airport attack.
Police recovered a Kalashnikov assault rifle next to the dead attacker.
An unexploded bomb belt was also reportedly found at the terminal.
A suspect package was destroyed at the Vrije University in central Brussels – as the country’s Tihange nuclear power plant was evacuated.
Two people were arrested by armed police at the city’s Noord railway station hours later – as officials said they feared “people are still at large”.
As the city went into lockdown, Belgian Prime Minister Charles Michel condemned the attacks as “cowardly” on what he described as “a black day” for the nation.
“What we feared has happened, we were hit by blind attacks,” he said.
“This is a dark moment for our nation. We need calm and solidarity.”
Zach Mouzoun, who arrived at the airport on a flight from Geneva about 10 minutes before the first blast, told France’s BFMTV: “It was atrocious. The ceilings collapsed. There was blood everywhere, injured people, bags everywhere. We were walking in the debris. It was a war scene.”