Prime Minister Justin Trudeau condemned the attacks in Brussels this morning, as his cabinet said they see no imminent threats to Canadians on their soil.

"I am outraged and deeply saddened by the news that so many have been killed and injured in terrorist attacks targeting the people of Brussels, Belgium," Trudeau said in a statement.

Air Canada also warned that flights to the Belgian city may be cancelled and security was beefed up at one of Toronto’s main transportation hubs. At least one Twitter post indicated the cancellation of a Canadian school trip to the European capital.

Trudeau said his thoughts were with the victims as Canada stands with Belgium and the European Union.

Foreign Minister Stephane Dion, speaking in Ottawa, called it a "black Tuesday."

"Hearing the screams of children in the smoke of the Brussels metro only strengthens our resolve to combat terrorism in all its forms, and increases our solidarity with the people of Belgium and the whole of Europe," Dion said.

Increased vigilance

Public Safety Minister Ralph Goodale said the threat level will not be changed in wake of the attacks, which remains at medium, where its been since October 2014.

"There is no information available to RCMP or CSIS that would lead us to any change in threat levels," he said.

But Goodale told Canadians to be vigilant.

"Be aware of your circumstances and your surroundings. If you notice anything that you consider to be unusual or out of the ordinary then you should report that circumstance immediately to your local police," he said.

Dion said he has "no reports of any Canadian citizens being affected by the incidents."

Belgian officials said the casualty toll from three explosions in the capital was 31 dead and 187 injured.

Belgian Health Minister Maggie de Block said 11 people were dead and 81 injured in twin explosions at the Brussels airport. The Brussels mayor said at least 20 people died and 106 were injured in the attack on the Maelbeek subway station, which is close to the European Union headquarters.

In an advisory posted on its website early Tuesday, Global Affairs said while there was no nationwide advisory in effect for Belgium, Canadians should exercise a "high degree of caution due to the current elevated threat of terrorism."

More than 200 flights to Brussels were diverted or cancelled, according to flight tracking service Flightradar24.

Air Canada spokesman Peter Fitzpatrick said the airline’s staff and crew in Brussels were safe and sound and that one flight had been diverted to Paris.

In Toronto, security and police presence was beefed up at Union Station, according to Metrolinx spokeswoman Anne Marie Aikins.

"We do take special precautions with Union Station because it is our largest transportation hub in the country," she said.

"When things like this happen around the world, we take extra vigilant precautions."

Tightened airport security

The Paris airport authority said security was tightened at all local airports soon after the Brussels explosions on Tuesday morning. Airports in London, Prague, Amsterdam, Vienna, and many others, also saw increased security.

The explosions, which the Brussels prosecutor’s office calls terror attacks, came just days after the main suspect in the deadly Nov. 13 Paris attacks was arrested Friday in the city.

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 today’s attacks.

Belgium has 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.

— With files from The Associated Press