At least 18 people are dead after one of Canada's worst mass shootings, in which a gunman dressed as a police officer went on a more than 12-hour killing spree, authorities said.

The suspected shooter, who is also dead, donned a police uniform and drove around in what appeared to be a police cruiser as he set fires to homes and went on a gun rampage starting in the small rural town of Portapique in Nova Scotia.

A police officer was among the dead in the assault that began Saturday night. Authorities said the gunman may have targeted his first victims, then attacked randomly.

"This is one of the most senseless acts of violence in our province’s history," said Nova Scotia Premier Stephen McNeil.

Here's what we know:

What happened in Nova Scotia shooting?

Prime Minister Justin Trudeau said Monday the death told had risen to 18.

"We are a country that stands united in our effort to defeat a pandemic, to save lives and to help each other make it to a better day. But yesterday, we were jolted from that common cause by the senseless violence and tragedy in Nova Scotia," Trudeau told reporters Monday.

The assault began late Saturday as Royal Canadian Mounted Police warned residents in the area to stay home with their doors locked.

Sunday morning, police tweeted a photo of Gabriel Wortman, 51, who they warned was "armed and dangerous."

As Wortman moved through the area heading south, police continued to tweet his location. They also shared a photo of his vehicle, which appeared to be a police cruiser.

At one point, there was an exchange of gunfire between the suspect and police, said RCMP Chief Superintendent Chris Leather.

By 11 a.m. Sunday local time, police said Wortman had switched cars. The pursuit spanned more than 50 miles to a gas station in Enfield, where he was shot dead by RCMP officers. Nova Scotia's Serious Incident Response Team, independent of the police force, said it was investigating the shooting.

Leather said Monday there were at least 16 crime scenes across central and northern Nova Scotia.

"We're relatively confident we've identified all the crime scenes. However we have unable to fully examine all the crime scenes," he said. “We have had five structure fires, most of those being residences, and we believe there may be victims still within the remains of those homes which burnt to the ground."

Officers had been patrolling the streets of the small town of Portapique throughout the night, and by morning helicopters were flying overhead, said Christine Mills, a resident of the area.

"It's nerve-wracking because you don't know if somebody has lost their mind and is going to beat in your front door," she said.

Who are the victims of the shooting?

Police said several bodies were found inside and outside a home in Portapique, which police believe to be the first scene.

“The vast majority of Nova Scotians will have a direct link with one more more of victims. The entire province and country is grieving right now as we come to grips with something that is unimaginable,” Trudeau said.

Constable Heidi Stevenson was identified as the dead police officer. The mother of two was a 23-year veteran of the Royal Canadian Mounted Police.

Trudeau said Stevenson "died protecting others" and "answering the call of duty."

The Nova Scotia Teachers Union said teacher Lisa McCully was also among the dead.

Two health care workers at local nursing homes were also among those killed, according to VON Canada, a long-term health care company, which identified them as Heather O’Brien, a licensed practical nurse, and Kristen Beaton, a continuing care assistant.

Trudeau said a virtual vigil would be held Friday for the entire country to mourn and celebrate the victims' lives.

Who is the suspected shooter?

Wortman was said to have lived part time in Portapique and part time in Halifax.

Tom Taggart, a local lawmaker, said he had spoken to Wortman a few times concerning municipal issues but didn't know him well.

Taggart described knowing Wortman’s “lovely big home” on Portapique Beach Road.

A Gabriel Wortman is also listed as a denturist – a person who makes dentures – in the city of Dartmouth, near Halifax, according to the Denturist Society of Nova Scotia website.

Police have not said what they believe Wortman's motive to be but said the initial attack was targeted.

“That fact that this individual had a uniform and a police car at his disposal certainly speaks to it not being a random act,” Leather said. He said police believe Wortman acted alone, and many of the victims did not know the suspect.

Police were also looking into whether there was any connection to the coronavirus pandemic, but Leather said no link has been found.

Trudeau asked the media not to give the gunman "the gift of infamy" by naming him or sharing his photo.

Mass shootings are rare in Canada

Before the weekend's shooting, a rampage at Montreal’s Ecole Polytechnique college in 1989 was the worst mass shooting in Canada in modern history.

After a gunman killed 14 women then himself, the country overhauled gun-control laws. The country requires training, personal risk assessment, references, spousal notice and a criminal background check to purchase a firearm. Unregistered handguns and rapid-fire weapons are banned, too.

Trudeau vowed Monday to renew efforts to ban assault-style weapons across Canada that was interrupted amid the coronavirus pandemic. "We have every intention of moving forward on that measure and potentially other measures when the parliament returns," Trudeau said.

Contributing: The Associated Press