Prime Minister Justin Trudeau is calling the attack on a gay nightclub in Florida an act of domestic terror.

Trudeau says he was "shocked and saddened" to learn so many people were killed and injured following the mass shooting in Orlando.

Trudeau says that while authorities are still investigating and not all details have been confirmed, it is "appalling that as many as 50 lives may have been lost to this domestic terror attack targeting the LGBTQ2 community."​

Trudeau says he and his wife, Sophie Grégoire Trudeau, are offering condolences and prayers to the families and friends of those lost and wish full recovery to those who were injured in the attack.

Trudeau says they stand in solidarity with Orlando and the LGBT community and grieve with their friends in the United States and Florida.

Public Safety Minister Ralph Goodale wrote on Twitter that he is shocked by the mass shooting and that Canadians condemn such violence.

U.S. police say the attack happened early Sunday morning, when a gunman wielding an assault-type rifle and a handgun opened fire inside a crowded gay nightclub. He later died in a gunfight with police.

Goodale says his thoughts and prayers are with the loved ones of the victims.

Governor General David Johnston called the deadly attack "appalling" and called on Canadians to "remain committed to diversity."

The Royal family in Britain tweeted a message of support from the Queen, who is celebrating her 90th birthday in London.

Ontario Premier Kathleen Wynne wrote on Twitter that her thoughts are with the LGBTQ2S community.

B.C. Premier Christy Clark said on Twitter that she is "incredibly saddened by the evil brutality" of the Florida shooting, and that her province "stands united with [Orlando] against terror and hate."

Toronto Mayor John Tory tweeted his condolences and announced that the city's Toronto sign would be lit in rainbow colours to honour the victims, who were slain at a gay nightclub during Pride month in what at least one U.S. congressmen has speculated is a hate-fuelled attack.

Trudeau's senior political strategist Gerald Butts called the shooting "horrible."

Sunday's violence is considered the worst mass shooting in U.S. history.

With files from CBC News