Canadian police have admitted that they failed to issue a timely public alert about the gunman who killed 22 people across eastern Nova Scotia, after facing mounting criticism for using social media to notify the residents instead.

The shooter, 51-year-old Gabriel Wortman, began his rampage on Saturday night. The massacre continued in several small Nova Scotian towns and ended around noon on Sunday.

During the worst mass shooting in the country's history, the Nova Scotia provincial detachment of the Royal Canadian Mounted Police (RCMP) sent a series of tweets to about 90,000 followers warning that there was an active shooter in the area.

Police set up two barriers around the initial crime scene in Portapique on Saturday night.

But they didn't realize until between 7am and 8am the next morning that the shooter had disguised himself as an RCMP officer and was driving a vehicle resembling a police car.

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Canadian police (pictured on Thursday) have admitted that they failed to issue a timely public alert about the gunman, who killed 22 people across eastern Nova Scotia, after facing mounting criticism for using social media to notify the residents instead

During the worst mass shooting in the country's history, the Nova Scotia provincial detachment of the Royal Canadian Mounted Police (RCMP) sent a series of tweets to about 90,000 followers warning that there was an active shooter in the area

Police said they started the process of issuing the alert but it took several hours to make its way up the chain of command.

Nova Scotia RCMP Chief Superintendent Chris Leather told reporters on Wednesday that 'Nova Scotia emergency management officials contacted the RCMP to offer the use of the public emergency alerting system'.

'We were in the process of preparing an alert when the gunman was shot and killed by the RCMP.'

Leather defended the use of social media, saying he was 'very satisfied' with the messaging, which he said the media helped spread, and that the 'communications being provided were the best and clearest information that could be provided'.

At 9.17am, authorities tweeted this image of the car that Wortman was driving

On Monday, Leather told reporters that the force felt it was a 'superior way to communicate' the threat in the community, but said the force would look into the matter.

Nova Scotia Premier Stephen McNeil said the province had not received a request from police for an emergency alert to be sent out.

Canadian authorities are still investigating what led Gabriel Wortman (pictured), 51, to shoot dead at least 19 people during a shooting spree in Nova Scotia

But some of the families and friends of the victims said a provincial warning system, which would have sent out text, radio and TV warnings, might have saved the lives of their loved ones.

'I don't use Twitter, and I don't know anyone that does use Twitter,' Nick Beaton said in an interview broadcast by CTV News.

Beaton's wife, Kristen, a nurse and mother from Debert, was shot dead on Sunday while on her way to work.

Beaton said he would have never let his wife leave the house that morning had he known the gunman was still at large.

She was pregnant with the couple's second child.

'We never got the chance to tell family,' he said. 'We were going to tell them this week, she was going on vacation.'

Wortman's motive remains unknown. Police have said some of his victims were known to him, including his ex-wife and her new boyfriend, but others appear to have been chosen randomly.

Police are still piecing together the timeline of events, Leather said, adding more details could come on Thursday. Wortman did not possess a firearms license in Canada, he said.

Police initially said they believed there were 23 victims but Royal Canadian Mounted Police (RCMP) spokesman Daniel Brien later confirmed the death toll included 22 victims and the gunman.

Authorities have also cautioned that they are still investigating crime scenes, including more than five homes Wortman burned to the ground.

No details have been released about the type of gun used by Wortman or how it was obtained.

Bringing in stricter gun control measures was an election promise of Prime Minister Justin Trudeau's Liberals in the October 2019 federal election, and he told reporters on Tuesday the legislation had been 'almost ready to go' when the novel coronavirus crisis hit.

Police initially said they believed there were 23 victims but RCMP spokesman Daniel Brien later confirmed the death toll included 22 victims and the gunman. Police have cautioned that they are still investigating crime scenes, including more than five homes Wortman burned down

'The tragedy in Nova Scotia simply reinforces and underlines how important it is for us to continue to move forward on strengthening gun control in this country,' Trudeau said. 'We will do that at the appropriate time.'

Meghan Nearing, a resident of the area where many of Wortman's victims lived, was home with her son on Saturday night and heard about the shootings, but did not know the gunman was still active when she woke up the next morning.

'There was nothing, no alert, so I thought everything was OK,' she said, speaking not far from where RCMP Constable Heidi Stevenson was shot and killed by Wortman on Sunday.

'Little did I know he was in my town when I was thinking that.'