Canada's worst mass shooting occurred in the wake of an assault on the gunman's girlfriend, who survived the attack, police say.

Key points: The suspect's girlfriend hid overnight in the forest following the confrontation

The suspect's girlfriend hid overnight in the forest following the confrontation At 6:30am, she emerged from hiding, called 911 and gave police detailed information about the suspect

At 6:30am, she emerged from hiding, called 911 and gave police detailed information about the suspect Canada overhauled its gun laws after Marc Lepine shot 14 women and himself in 1989

Royal Canadian Mounted Police superintendent Darren Campbell said the weekend shooting rampage that left 22 people dead in communities across central and northern Nova Scotia started with an assault by the suspect on his girlfriend.

"She did manage to escape. That could well have been the catalyst of events," Mr Campbell said.

Authorities are not discounting the suspect, who acted alone in the shooting spree, planned some of the murders.

Mr Campbell said the girlfriend hid overnight in the forest from 51-year-old Gabriel Wortman.

Several homes were on fire, including Wortman's, when police arrived at Portapique where he had lived.

The officers saw "several people who were deceased, some of which were lying in the roadway", Mr Campbell said.

Canadian police investigators search for evidence at the location where a police constable was killed. ( AP: Andrew Vaughan )

At about 6:30am, Wortman's girlfriend emerged from hiding in the woods, called 911 and gave police detailed information about the suspect including that he was driving a mock police car and was in police uniform, he added.

Police later started receiving 911 calls more than 55 kilometres away.

The suspect was shot dead at 11:26 on Sunday morning, about 13 hours after the attacks began.

The suspect's girlfriend is recovering and continues to cooperate with police.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 48 seconds 48 s A gunman impersonating a police officer killed several people in Nova Scotia.

'I'm just telling you, I've got guns in here'

"There seems to be a trail of individuals who had problems with Mr Wortman," Mr Campbell said.

John Hudson, who had known Wortman for about 18 years, said he had been purchasing used police vehicles at auctions and had once threatened him.

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He said Wortman was sometimes openly controlling and jealous of his long-time girlfriend.

"I didn't see him hitting her or anything like that," Mr Hudson said. "But I know they fought."

Mr Hudson recalled a bonfire party about 10 years ago when an argument between the two left the woman locked out of their home in rural Portapique.

"I was with her, trying to get her stuff out of there," Mr Hudson said.

"People had been drinking … and it was a crazy night … and he didn't want her to leave, but he wouldn't let her in the house."

Mr Hudson said at one point, Wortman removed the tires from the woman's vehicle and threw them into the ditch to prevent her from leaving.

"So, I went to get (her clothes) and what he said to me was: 'I don't want anyone in my house. If you come in my house, I'm just telling you, I've got guns in here.'"

Wortman, who owned a denture practice in the city of Dartmouth, near Halifax, lived part time in Portapique, according to residents.

His Atlantic Denture Clinic had been closed the past month because of the coronavirus pandemic.

The suspect was shot to death at 11:26 on Sunday morning, about 13 hours after the attacks began. ( AP: Andrew Vaughan/The Canadian Press )

Mass shootings are relatively rare in Canada. The country overhauled its gun control laws after Marc Lepine shot 14 women and himself at Montreal's Ecole Polytechnique college in 1989.

Before the weekend rampage, that had been Canada's worst mass shooting.

ABC/AP