Police say six people have been killed and eight wounded in a shooting at a Quebec City mosque that Canada's prime minister described as a terrorist act.
The shooting at the Quebec City Islamic Cultural Centre in the provincial capital happened during evening prayers on Sunday.
Two arrests have been made.
Quebec Provincial Police spokeswoman Christine Coulombe said some of the wounded were gravely injured and the age range of the dead was about 35 to 70.
She said one person was arrested at the scene and the other nearby in d'Orleans.
Thirty-nine people were in the mosque at the time of the attack, she added.
Prime minister Justin Trudeau and Quebec premier Philippe Couillard characterised the shooting as a terrorist act, which came amid heightened tensions worldwide over US president Donald Trump's travel ban on some Muslim countries.
Mosque president Mohamed Yangui said the shooting happened in the men's section of the mosque and he feared some victims were children.
He said he was not at the centre when the attack occurred, but obtained some details from people at the scene.
"We are sad for the families," he said.
In a statement, Mr Trudeau said: "We condemn this terrorist attack on Muslims in a centre of worship and refuge.
"It is heart-wrenching to see such senseless violence.
"Diversity is our strength and religious tolerance is a value that we, as Canadians, hold dear.
"Muslim-Canadians are an important part of our national fabric, and these senseless acts have no place in our communities, cities and country.
"Canadian law enforcement agencies will protect the rights of all Canadians and will make every effort to apprehend the perpetrators of this act and all acts of intolerance."
Quebec City police spokesman Constable Pierre Poirier said two suspects were arrested.
Mr Trudeau said on Twitter that he spoke to Mr Couillard and was being briefed by officials.
The prime minister said the government had offered "any & all assistance needed".
Mr Trudeau had earlier reacted to Mr Trump's visa ban for people from certain Muslim-majority countries by tweeting on Saturday: "To those fleeing persecution, terror & war, Canadians will welcome you, regardless of your faith. Diversity is our strength #WelcomeToCanada."
He also posted a picture of him greeting a Syrian child at Toronto's airport in late 2015.
Mr Trudeau oversaw the arrival of more than 39,000 Syrian refugees soon after he was elected.
Mr Couillard described the Sunday mosque attack as "barbaric violence" and expressed solidarity with the victims' families.
The mayor of Gatineau, Quebec, near Canada's capital of Ottawa, said there would be increased police presence at mosques around his city and in the US, the New York Police Department said it was stepping up patrols at mosques and other places of worship.
New York City Mayor Bill Blasio said on Twitter: "NYPD is providing additional protection for mosques in the city.
"All New Yorkers should be vigilant. If you see something, say something.
"Our prayers tonight are with the people of Quebec City as they deal with a terrible attack on a mosque.
"We must stand together."
In the summer of 2016 a pig's head was left on the doorstep of the Quebec Islamic Cultural Centre.
The incident occurred in the middle of Ramadan, when Muslims fast from dawn to sunset - practising Muslims do not eat pork.
Francois Deschamps, an organiser of a refugee support group in Quebec City, said the motive was unknown, but right-wing groups were very organised in Quebec City and distribute leaflets at the university and post stickers around town.
Mr Deschamps said he has personally received death threats after starting a refugee support group on Facebook and people had posted his address online.
"I'm not very surprised about the event," he said.
Canada is generally very welcoming towards immigrants and all religions, but less so in the French-speaking province of Quebec.