In what is believed to be Canada's worst mass shooting, a gunman has killed 16 people - including a female police officer - after disguising himself as a policeman, the BBC reports.

The shootings started on Saturday, with the murderous rampage lasting 12 hours and ending in a car chase.

Police have stated that the suspect randomly shot people at different locations in Nova Scotia.

The gunman was killed during a confrontation with police.

When the attacks began, residents of the rural town of Portapique were advised to lock themselves indoors, after it was also reported that the gunman was driving around in what looked like a police car.

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Writing in a tweet, the Royal Canadian Mounted Police Constable (RCMP) identified the suspect as Gabriel Wortman, and stressed that he was "NOT employed by the RCMP but he may be wearing an RCMP uniform".

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On Sunday, authorities were still trying to establish the final death toll on Sunday and warned that there could be more victims.

One of those shot dead was RCMP officer Heidi Stevenson, who had served in the forced for 23 years.

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Nova Scotia RCMP Commanding Officer, Assistant Commissioner Lee Bergerman posted a tribute to the fallen officer in a Facebook post, writing:

"Today is a devastating day for Nova Scotia and it will remain etched in the minds of many, for years to come.

"What has unfolded overnight and into this morning is incomprehensible and many families are experiencing the loss of a loved one.

"That includes our own RCMP family. It is with tremendous sadness that I share with you that we lost Cst. Heidi Stevenson, a 23-year veteran of the Force who was killed this morning, while responding to an active shooter incident.

"Heidi answered the call of duty and lost her life while protecting those she served."

Commissioner Bergerman added: "Two children have lost their mother and a husband his wife. Parents lost their daughter and countless others lost an incredible friend and colleague."

The commissioner also revealed that another RCMP officer was injured and is in hospital receiving treatment of non-life threatening injuries.

RCMP Commissioner Brenda Lucki later told CBC News that she believed the gunman had an initial "motivation" at the start of his attack, but then "turned to randomness".

Canadian Prime Minister Justin Trudeau wrote in a tweet: "Our hearts go out to everyone affected by the shooting in Nova Scotia. To the Portapique community, we’re keeping all of you in our thoughts. And on behalf of all Canadians, I want you to know that we’re here for you - and we’ll be here for you in the days and weeks ahead."

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Bill Blair, Minister of Public Safety and Emergency Preparedness, said in a statement:

"In the coming days, the RCMP will continue to share information about what happened today. I know the people of Nova Scotia will band together to heal and mourn those who were lost. All Canadians will stand with them."

Canada: At least 16 dead in country's deadliest mass shooting