(AP) -- Explosions rocked the Brussels airport and the subway system Tuesday, killing at least 28 people and injuring many others just days after the main suspect in the November Paris attacks was arrested in the city, police said.

Witnesses described the ceiling caving in and blood everywhere after two explosions in the departure hall at the Brussels airport. All flights were canceled, arriving planes and trains were diverted and Belgium's terror alert level was raised to maximum. Authorities told people in Brussels to stay where they were, bringing the city to a standstill. Security was also tightened at all Paris airports.

European security officials have been braced for a major attack for weeks, and warned that Islamic State was actively preparing. The arrest of Salah Abdeslam in Brussels last week heightened those fears, as investigators said many people involved in the Nov. 13 Paris attacks that killed 130 people were still on the loose. After Abdeslam was arrested, Belgian Foreign Minister Didier Reynders said authorities learned he had created a new network around him and had access to several weapons, though there was no immediate indication that he or the Islamic State group had any involvement in Tuesday's attacks.

Belgian media reported 13 people were killed at the airport. It was not clear whether any died in the metro explosion. 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 blood from victims.

"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 the Maelbeek subway station, not far from the headquarters of the European Union, rescue workers set up a makeshift treatment center in a local pub. Dazed and shocked morning travelers 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 that there appeared to have been just one explosion, in a car that was stopped at Maelbeek.

First responders ran through the street outside with two people on stretchers, their clothes badly torn.

The explosions at the airport hit at the middle of the busiest time there. Smoke was seen billowing out of the terminal.

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.

"I knew it was an explosion because I've been around explosions before," said Denise Brandt, an American woman interviewed by Sky television.

"I felt the explosion, the way it feels through your body. And we just looked at each other and I said 'Let's go this way.' It was over there. There was just this instinct to get away from it. Then we saw people running, crying, toward us. So I knew we were going in the right direction and away from it. "

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.

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Associated Press Writers Raf Casert in Brussels and Angela Charlton and Lori Hinnant in Paris contributed to this report.