At least 26 people have been killed after a terrorist suicide attack ripped through Zaventem Airport in Brussels and another blast hit a city metro station.
Shots were fired and Arabic shouted before the two airport bomb blasts, according to Belgian news agency Belga.
Maalbeek metro station was targeted in a separate attack during the morning rush hour.
An image showed an empty pushchair surrounded by debris from an explosion at the airport, while children could be heard screaming after the underground blast.
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 attack on the airport.
Brussels fire brigade spokesman Pierre Meys said 11 people died and 35 were wounded in the twin blasts.
At least 15 people were killed and 55 injured – 10 critically – in the metro explosion, according to public transport operator STIB.
As the city went into lockdown, Belgian Prime Minister Charles Michel condemned the “violent” 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.”
Video and images on social media showed smoke rising from an airport building and shattered windows.
Confused and shocked passengers fled the terminal to safety as they were evacuated by armed police.
Footage also showed ceiling tiles littered across the floor and strewn black luggage belts, cases and bags at a check-in desk.
According to reports, the first blast took place near a counter where customers pay for overweight baggage – and the second near a Starbucks at the airport.
Anthony Deloos, who works for the baggage handling firm Swissport, said he “jumped into a luggage chute to be safe”.
:: Special Programme: Brussels Attacks on Sky News at 7pm tonight
The attacks follow the dramatic arrest of Paris attacks suspect Salah Abdeslam in the Belgian capital on Friday – four months after November’s terror in the French capital that left 130 people dead.
Authorities have said it is unclear if he is linked to Tuesday’s suspected coordinated attacks.
Sky’s Alex Rossi had just checked-in at the airport when he heard “two very, very loud explosions”.
“I could feel the building move. There was also dust and smoke as well,” he said.
“I went towards where the explosion came from and there were people coming out looking very dazed and shocked.
“There is a great deal of confusion here. Certainly there are a number of very upset, as you might imagine, very frightened people.”
He added: “There are fears that there might be other attackers.”
Some 225 extra soldiers have been deployed to the city to beef up security in the aftermath of the terror.
Eurostar services to and from Brussels have been suspended – and all trains to the airport cancelled which has been closed until further notice.
All public transport has been shutdown with Belgium hiking its terror threat to its highest level following the strikes.
Brussels residents have been urged to “stay where you are”, and the European Commission, the executive arm of the European Union, has told staff to stay at home.
Security at key locations and transport hubs has also been stepped up across the UK, Netherlands, France and Germany.
London Mayor Boris Johnson said “there may be one UK casualty”, while his counterpart in Paris, Anne Hidalgo, announced the Eiffel Tower will be lit up this evening with Belgium’s national colours.
One of Islam’s leading institutions, Al Azhar, condemned the “heinous” attacks as a violation of “the tolerant teachings of Islam”.
