At least 18 people have been killed after a gunman disguised as a Mountie went on a 12-hour rampage across Nova Scotia, making it the deadliest such attack in Canadian history.

The suspect – identified by police as Gabriel Wortman, 51 – was tracked down to a gas station on Sunday after shooting “multiple victims”, police said. It was initially announced that he was arrested, but police have since said he has died.

Earlier on Sunday, it was reported the suspect was driving a car that looked like a police vehicle while wearing a uniform. Wortman was not connected to the Royal Canadian Mounted Police (RCMP).

The police also confirmed the man was dressed up as a Mountie during at least part of his rampage.

“It was not a random act,” RCMP Chief Superintendent Chris Leather said on Sunday based on the man at one point using a police uniform and car in his attack.

Constable Heidi Stevenson, a 20-year veteran, was killed in the line of duty when responding to the active shooter situation, RCMP confirmed during a press conference.

Officers were first called to the scene at Portapique on Saturday evening and found numerous casualties inside and outside of the home, a spokesperson said. Wortman was not located in the home at the time.

“Our priority was to secure the area, and we were able to secure the area,” the spokesperson said. “And then we began the search for the suspect.”

The gunman’s shooting spree then took off across the province from Saturday into Sunday.

His targets appeared to include some random bystanders, said Mr Leather. “We believe it to be one person who is responsible for all the killings and that he alone moved across the northern part of the province and committed what appears to be several homicides.”

Nova Scotia premier Stephen McNeil addressed the investigation on Sunday afternoon.

“I never imagined when I went to bed last night that I would wake up to the horrific news that an active shooter was on the loose in Nova Scotia. This is one of the most senseless acts of violence in our province’s history,” Mr McNeil said.

Prime minister Justin Trudeau also spoke about the incident outside his home on Sunday. “My heart goes out to everyone affected in what is a terrible situation,” he said. “I want to thank the police for their hard work, and people for cooperating with authorities.”