Two terror attacks hit the Zaventem Airport and another targeted Maelbeek Metro Station on Tuesday in Belgian capital Brussels, killing 31 people and wounding 200.
The attacks were claimed by the DAESH terrorist organisation.
At least 11 people had been killed in the airport explosions while Brussels mayor Yvan Mayeur said "around 20" died by an explosion at the metro station.
"They came in a taxi with their suitcases, their bombs were in their bags," Zaventem mayor Francis Vermeiren said.
"They put their suitcases on trolleys, the first two bombs exploded. The third also put his on a trolley but he must have panicked, it didn't explode."
Witnesses at the airport said shots were also heard during the incident, meanwhile public broadcaster VRT said a Kalashnikov assault rifle was found next to the body of an attacker at the airport.
Belgian security services found and destroyed a discarded third bomb belt which was found at the Brussels airport.
The broadcaster said the bomb squad was additionally checking a suspect package at the University of Brussels.
Media sources said the blasts took place in the departures lounge and cited reports that it had occurred near the American Airlines desk. American Airlines said none of its employees were reported injured in the explosions.
Local media showed security camera footage of three young men pushing luggage trolleys through the airport, two of whom are now suspected to have blown themselves up.
Police issued a warrant for the third suspect involved in the bombing at the airport, calling for information as they issued a photograph of a man dressed in white and wearing a hat as he pushed a luggage trolley.
Social media showed pictures of smoke rising from the departure hall where all windows had been shattered by the blast. Passengers were seen running away down a slipway from the departure lounge.
Belgian media said rail traffic to the airport was suspended. The airport said it had cancelled all flights and the complex had been evacuated.
— Brussels Airport (@BrusselsAirport) March 22, 2016
Shortly afterwards, another explosion was heard at the Maelbeek metro station in Brussels, close to the EU institutions. Brussels mayor Yvan Mayeur said "there are some 20 people dead and 106 people injured" in the metro station attack, adding that "17 people are severely injured."
STIB also announced on Twitter that the metro was closing. An additional 225 soldiers have been sent into the city and the Belgian Crisis Centre has appealed to the population: "Stay where you are."
The European Commission locked down its staff, the vice president in charge of personnel tweeted, but a spokesman for officials working in the European Parliament nearby said the legislature was working normally.
Belgium hiked its terror threat to its highest level after the deadly explosions, Interior Minister Jan Jambon said. The alert level was raised from three to a maximum of four, and was applied across the country.
Belgian Prime Minister Charles Michel said on Tuesday that the "blind, violent and cowardly" attacks on Brussels airport and the metro system were a "black day" for the country and had left many dead.
"This is a day of tragedy, a black day," Michel said on national television. "Two attacks took place this morning in Zaventam airport and Maalbeek metro station, blind, violent, cowardly attacks," Michel said.
"There are many dead and many wounded, some of them seriously," he said.
Federal prosecutor Frederic Van Leeuw, sitting alongside Michel, said that of the two blasts at the airport "one was probably caused by a suicide bomber."
An official from the Gasthuisberg hospital in Leuven, Marc Decramer, said in an interview that the hospital is treating 11 people with serious injuries, three of them in critical condition since most of the wounded had fractures and deep cuts caused by flying glass and nails.
Security tightened across Europe
Dutch counter-terrorism officials said on Tuesday they were boosting security at national airports and tightening controls on the southern border with Belgium amid a series of blasts in Brussels.
Meanwhile, security measures have been reinforced at the Charles De Gaulle airport in Paris, an airport source told AFP. Additional patrols were also dispatched at Orly airport in southern Paris and the southern city of Toulouse.
After an emergency meeting with President Francois Hollande, France decided to deploy 1,600 additional police officers to bolster security at its borders and on public transport, French Interior Minister Bernard Cazeneuve said.
A total of 400 additional police officers will boost security in the greater Paris area, and military patrols will be refocused on public transport sites, the minister said.
London's Gatwick airport stepped up security as British Prime Minister David Cameron prepared to hold an emergency cabinet meeting on the attacks.
German police on Tuesday arrested three people in a car with a Belgian license plate close to the border with Austria. An investigation has been launched into whether they had planned to carry out an attack, a police spokesman stated.
"Investigations have been launched into the suspected planning of a serious criminal act against the state because there was notification of that," the spokesman said.
He said there was no evidence so far that the three suspects had any connection with the deadly Brussels attacks.
German authorities also stepped up security measures at airports, train stations and the borders with Belgium, France, the Netherlands and Luxembourg, a spokesman for the federal police said on Tuesday.
An additional police presence was noticeable at Frankfurt Airport and train station on Tuesday morning, a Reuters eyewitness said.
Danish police said they had increased patrols at Copenhagen Airport and other key points in the city.
Police in Sweden said they had reinforced their presence at airports and taken increased security measures at other public places.
Finnish Interior Minister Petteri Orpo said on Twitter "Finnish security officials have increased monitoring at Helsinki-Vantaa airport."
Suomen turvallisuusviranomaiset tehostaneet valvontaa mm. Helsinki-Vantaan lentokentällä.
— Petteri Orpo (@p_orpo) March 22, 2016
Eurostar also cancelled trains running to and from Brussels. "No trains are currently running to or from Brussels Midi," the high speed rail service said on its Twitter feed. "Brussels customers are advised to postpone, and not come to station.''
What do we know so far?
- Two explosions hit Zaventem Airport, caused by suicide bomber
- Another explosion hits Maelbeek metro station near EU institutions
- At least 31 people confirmed dead, 200 injured
- DAESH terrorist organisation claimed responsibility for the attacks
- Gunfire reportedly heard before explosions
- Airport suspends all flights, airport evacuated
- Belgian Interior Minister raises terror threat level to high
- Metro stations in Brussels closed
- European Commission locks down its staff
- Netherlands, France, UK, Germany, Denmark, Sweden, Finland tightens security
- Eurostar cancels trains to Brussels
- 225 soldiers deployed to Brussels
- Germany arrests three suspects driving Belgian car