Canada will respond to a "despicable act of terror" with open hearts and a show of unity, an emotional Prime Minister Justin Trudeau said Monday in the wake of the deadly shooting at a Quebec mosque.

Delivering a formal statement in the House of Commons, Trudeau said the shooting that left six worshippers dead is an act of terror committed against Canada and all Canadians. Speaking directly to the country's one million Muslims, he reassured them of their valued place in Canadian society.

"We are with you. Thirty-six million hearts are breaking with yours," he said. "Know that we value you, you enrich our shared country in immeasurable ways. You're home."

Trudeau urged Canadians not to be intimidated by Sunday's attack, or those who use violence to instill fear and division.

"They aim to divide us, to sow discord and plant hatred," he said. "We will not close our minds. We will open our hearts."

PM Justin Trudeau reads a statement in the House of Commons, calling the shootings a terrorist action, and vows to get to the bottom of the Quebec City attack. 5:16

Four party leaders delivered statements before the House rose for a minute's silence to honour the victims.

Interim Conservative Leader Rona Ambrose called the attack a "sad reminder" that Canada is not immune to terrorism and must remain vigilant. She said the shooting struck the heart of a fundamental freedom in Canada: to practise one's faith in safety and security.

"An attack against a place of worship, against people praying in a mosque is an attack on these very freedoms," she said. "It negates the principles on which Canada was founded."

NDP Leader Tom Mulcair said the shootings have shaken Canada to its very core, calling for all Canadians to unite against the forced of hatred, bigotry and Islamophobia.

"This is not the Canada we believe in, it's not the type of society we want to live in," he said. "Canada is a country of diversity, peace and inclusion. We cannot, and we will not, tolerate hate and violence."

Trudeau will travel to Quebec City later Monday to attend a vigil for the victims. He will be accompanied by Ambrose, Mulcair and Public Safety Minister Ralph Goodale.

Opposition Leaders Rona Ambrose, Thomas Mulcair, and Elizabeth May all express their grief and offer condolences to the victims of the Quebec City shootings. 3:37

Green Party Leader Elizabeth May's office said she planned to attend the vigil as well.

Trump offers assistance

Messages of shock, support and solidarity are flooding in from across the country and around the world in response to the attack.

U.S. President Donald Trump called Trudeau to express his condolences to the prime minister and Canadians. He also offered to provide any assistance as needed, according to the PMO.

The Canadian flag atop the Peace Tower is at half-mast in honour of the victims.

During a news conference Monday, the RCMP said the motives behind the mass shooting aren't clear.

Trudeau was quick to condemn it as a "terrorist attack" on Muslims.

"While authorities are still investigating and details continue to be confirmed, 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," Trudeau said in a statement released Sunday evening.

Public Safety Minister Ralph Goodale talks to reporters about the Quebec City shootings and says Canada needs to get 'very good at counter radicalization'. 3:04

Pope offers prayers

Pope Francis offered his prayers, and the city of Paris plans to dim lights on the Eiffel Tower at midnight in memory of the victims.

Russian President Vladimir Putin offered condolences to Trudeau on Twitter.

"Accept my deep condolences in connection with the tragedy in Quebec. ... The murder of people who gathered for a prayer in a mosque is shocking by its degree of violence and cynicism."

Bruce Heyman, the former U.S. ambassador to Canada, said he and his wife were saddened by the senseless attack.

.<a href="https://twitter.com/vshey">@vshey</a> and I are saddened by the senseless attack on the innocent in Quebec last night & send our condolences to the families and community —@BruceAHeyman

New York City Mayor Bill de Blasio said the "awful attack" is not an outlier, noting a mosque in Texas that was burned to the ground.

The mayor of London, England, Sadiq Khan, issued a message of defiance. "London stands with the people of Quebec. Hate & violence will not defeat us. Those who seek to divide us will fail."

London stands with the people of Quebec. Hate & violence will not defeat us. Those who seek to divide us will fail. <a href="https://t.co/H9ttOvHll9">https://t.co/H9ttOvHll9</a> —@SadiqKhan

Elizabeth Moore Aubin, the U.S. chargé d'affaires, issued a statement on behalf of all Americans offering "deepest and most heartfelt condolences."

"The United States is determined to fight terrorism and stands ready to assist the Canadian government as it deals with the aftermath of this tragic event."

The flag on Parliament Hill's Peace Tower flies at half-mast Monday in honour of the victims of the mosque shooting in Quebec City. (Adrian Wyld/Canadian Press)

During a news conference Monday afternoon, Goodale said the investigation was in its early stages and he would not speculate on possible motives for the attack.

The public safety minister also announced that the deadline to apply for funding from the Security Infrastructure Program would be extended beyond the Jan. 31 deadline to allow for additional applications. No new deadline has been set.

The program provides financial support to places of worship, provincially recognized schools and community centres so they can improve security around their buildings. Funding supports the cost of items such as gates, cameras, security assessments and some construction costs.

According to Public Safety Canada, the Quebec City mosque at the centre of Sunday's events had not applied for funding under the program.