Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe immediately tightened security as a fleet of emergency vehicles roared in to handle the carnage at the Brussels airport.
The explosions, which the Brussels prosecutor's office called terror attacks, came just days after the main suspect in the deadly Nov. 13 Paris attacks was arrested Friday in Brussels. After his arrest, 26-year-old Salah Abdeslam told authorities he had created a new network and was planning new attacks.
There was no immediate claim of responsibility for Tuesday's attacks.
Belgian media reported that 13 people were killed at the airport. Brussels police spokesman Christian De Coninck said some people also died at the subway station but he had no exact numbers yet on the dead or injured.
At the airport, two explosions splattered blood across the departure lounge and collapsed the ceiling. The explosions hit during the busy morning rush. Smoke was seen billowing out of the terminal.
Anthony Deloos, an airport worker for Swissport, which handles check-in and baggage services, said the first explosion took place near the Swissport counters where customers pay for overweight baggage. He and colleague said second blast hit near the Starbucks cafe.
"We heard a big explosion. It's like when you're in a party and suddenly your hearing goes out, from like a big noise," Deloos said, adding that shredded paper floated through the air as a colleague told him to run.
"I jumped into a luggage chute to be safe," he said.
Tom De Doncker, 21, check-in agent intern, was near the site of the second explosion.
"I saw a soldier pulling away a body," he said. "It felt like I was hit too" from the concussion of the blast.
All flights from Brussels were canceled, arriving planes and trains were diverted. Authorities told people in Brussels to stay where they were, bringing the city to a standstill. Airport security was also tightened in Paris, London and other European cities.
European security officials have been bracing for a major attack for weeks, and warned that the Islamic State group was actively preparing to strike. Abdeslam's arrest on Friday heightened those fears, as investigators said many more people were involved in the Nov. 13 attacks that killed 130 people in Paris than originally thought, and that some are still on the loose.
Zach Mouzoun, who arrived on a flight from Geneva about 10 minutes before the first blast, told BFM television that the second, louder explosion brought down ceilings and ruptured pipes, mixing water with victims' blood.
"It was atrocious. The ceilings collapsed," he said. "There was blood everywhere, injured people, bags everywhere."
"We were walking in the debris. It was a war scene," he said.
Near the entrance to Brussels' Maelbeek subway station, not far from the headquarters of the European Union, rescue workers set up a makeshift medical treatment center in a pub. Dazed and shocked morning commuters streamed from the metro entrances as police tried to set up a security cordon.
"The Metro was leaving Maelbeek station for Schuman when there was a really loud explosion," said Alexandre Brans, 32, wiping blood from his face. "It was panic everywhere. There were a lot of people in the metro."
Francoise Ledune, a spokeswoman for the Brussels Metro, said on BFM television there appeared to have been just one explosion on the subway in a car that was stopped at Maelbeek.
At the airport, passengers fled as quickly as they could.
Amateur video shown on France's i-Tele television showed passengers including a child running with a backpack dashing out of the terminal in different directions as they tugged luggage, Another image showed a security officer patrolling inside a hall with blown-out paneling and what appeared to be ceiling insulation covering the floor.
Marc Noel, 63, was about to board a Delta flight to Atlanta, to return to his home in Raleigh, North Carolina. A Belgian native, Noel says he was in an airport shop buying automobile magazines when the first explosion occurred 50 yards away.
"People were crying, shouting, children. It was a horrible experience," he told AP. He said his decision to shop might have saved his life. "I would probably have been in that place when the bomb went off."
With three runways in the shape of a "Z," the airport connects Europe's capital to 226 destinations around the world and handled nearly 23.5 million passengers in 2015.
Passengers were led onto the tarmac and the crisis center urged people not to come to the airport.
In Paris, France's top security official said the country was immediately reinforcing security at airports, train stations and metros.