Airlines canceled hundreds of flights and European railways froze links with Brussels Tuesday after a series of bombs blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response.

Belgium locked down the capital, home to the headquarters of the European Union and NATO, and imposed its highest level of security alert after the explosions, which extinguished about 20 lives in the metro and another 14 in the airport, according to authorities in Brussels.

As passengers fled the smoking airport and the city-center Maalbeek metro station, where a train was blown apart, transport operators 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 closure of metro, bus and tram systems. Major railway stations were closed, too, the Brussels public prosecutor said.

Eurostar said all trains to and from Brussels had been halted.

"Our thoughts rest with anyone affected by the unfolding events in Bruokssels," it said in a statement.

The high speed train service Thalys, which links France and Belgium, said all its traffic, too, had been stopped.

The Brussels-Zaventem international airport is closed until 6am (0500 GMT) Wednesday, the airport said.

The airport shutdown forced more than 500 arrivals and departures to be canceled or diverted, according to the European Aviation Crisis Coordination Cell in Brussels, paralyzing air links with cities across Europe and other international airports.

"As a result of the attacks in Brussels, a number of other countries have increased security measures at airports. This could cause additional delays for passengers," the crisis cell said in a statement.

"All flights canceled 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 center urged people not to move. "No public transport. Stay where you are, also in schools, companies," it said on Twitter.

Forces tightened security at nuclear plants across the country, the Belga news agency said. "Vehicles are being checked with police and army on site," the agency added.

Belgium's neighbors France, Germany and the Netherlands reacted swiftly.

In France, where the November 13 Paris attacks that killed 130 people were intricately linked to jihadist networks in Belgium, an additional 1,600 police are being deployed to border crossings, airports, ports and train stations, said Interior Minister Bernard Cazeneuve.

People in France will need tickets or ID cards to access public transport areas, he said, and they may be frisked.

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.

In Germany, federal police said controls were being stepped up at the border with Belgium and at airports and stations.

The Netherlands, likewise, strengthened surveillance at the border with Belgium and ordered extra patrols at national airports and train stations.

"We are taking extra security measures as a precaution," the Dutch anti-terrorism services said in an online statement, notably stepping up police patrols at Amsterdam's Schiphol international airport, Rotterdam and Eindhoven.

London Gatwick, Frankfurt and Moscow airports raised security, too.

Across the Atlantic, police in New York said they were positioning counter-terrorism reinforcements to crowded areas and train stations "out of an abundance of caution". In Washington DC, canine sweeps and patrols and patrols were stepped up, also as a precaution.