Six people have been killed and eight injured in a shooting at a mosque in Quebec City, Canada in what Quebec's premier and Canada's prime minister called an "act of terrorism".

Two people have been arrested following the attack which took place in the men's section of the Quebec City Islamic Cultural Centre during Sunday evening prayers.

President of the mosque, Mohamed Yangui said he was worried that children might be amongst those killed.

He said he was not at the center when the attack occurred, but he got some details from people on the scene.

He said an estimated 60 to 100 people would have been there at the time of the shooting. "We are sad for the families," he said.

The attack comes amid heightened tensions worldwide over U.S. President Donald Trump's travel ban on certain Muslim countries.

"We condemn this terrorist attack on Muslims in a centre of worship and refuge," Trudeau said in a statement.

"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," he said.

"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."

Police said the mosque had been evacuated and things were under control.

Trudeau said on Twitter that he spoke to Quebec's premier and was being briefed by officials.

The prime minister said the government had offered "any & all assistance needed."

Public Safety Minister Ralph Goodale said on Twitter Sunday that he was deeply saddened by the loss of life. His office said no motive had been confirmed.

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. Practicing 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 are very organised in the area.

Deschamps said he has personally received death threats after starting a refugee support group on Facebook.

"I'm not very surprised about the event," Deschamps said.

Canada is generally very welcoming toward immigrants and all religions, but it's less so in the French-speaking province of Quebec.