Europe froze air and rail links to Brussels as the authorities tightened security in alarm over a series of deadly bomb blasts that ripped through the Belgian capital's airport and a city-centre metro station.
Belgium locked down the capital, home to the headquarters of the European Union and NATO, and imposed its highest level of security alert, as the toll rose to at least 21 people.
As passengers fled the smoking airport and the bomb-hit Maalbeek metro station, the public authorities shut down the airport, metro system, buses, trams and major railway stations in the capital.
"Our whole network is closed at the moment," the Brussels public transport operator STIB warned people on Twitter, confirming the shut-down of metro, bus and tram systems.
The Brussels-Zaventem international airport is closed until 6am (0500 GMT) tomorrow, the airport said.
The shutdown hit hundreds of flights scheduled to arrive and depart from the airport, halting more than 400 arrivals from across Europe and other international airports including New York and Dakar.
"All flights cancelled at #brusselsairport for the rest of the day. Avoid the surroundings of the airport," the airport said on Twitter.
"All our thoughts go to the victims of the horrible events that happened here at #brusselsairport this morning, their family and friends."
Belgium's crisis centre urged people not to move. "No public transport. Stay where you are, also in schools, companies," it said on Twitter.
Security forces tightened security at nuclear plants across the country, the Belga news agency said.
"Surveillance is stepped up with added security measures at nuclear plants," the agency reported. "Vehicles are being checked with police and army on site," the agency added.
The effects of the Brussels airport and train station closures rippled across Europe.
Major stations in Paris remained open but AFP correspondents saw many police patrolling in the city's Gare du Nord, from where Eurostar operates trains to London and Brussels.
Eurostar said all trains to and from Brussels had been halted.
"Following the incident in Brussels today we can confirm that Eurostar services are currently suspended on the Brussels route. Public transport in and around Brussels is also severely disrupted," Eurostar said in a statement.
"Our thoughts rest with anyone affected by the unfolding events in Brussels," it said.
European high speed train service Thalys said all its traffic, too, had been stopped.
Dutch anti-terrorism services NCTV said they were raising airport security and tightening southern border controls.
