An initial early morning emergency message popped up on the screens of mobile phones throughout Ontario.

People throughout the Canadian province of Ontario awoke on Sunday to an alarming alert of an “incident” at a nuclear plant just east of Toronto — only to later be told the message was a mistake.

The initial early morning emergency message popped up on the screens of mobile phones throughout the nation’s most populous province, saying an unspecified incident had occurred at the Pickering Nuclear Generating Station.

It added there had been no abnormal release of radioactivity and said people did not need to take protective action.

More than an hour later, Ontario Power Generation later sent a message saying the alert “was sent in error. There is no danger to the public or environment. No further action is required”.

The notification message also was pushed on to to television screens.

“The alert was issued in error to the public during a routine training exercise being conducted by the Provincial Emergency Operations Centre,” Ontario government Solicitor General Sylvia Jones said in a statement.

“The Government of Ontario sincerely apologises for raising public concern and has begun a full investigation to determine how this error happened and will take the appropriate steps to ensure this doesn’t happen again.”

Jim Vlahos, a 44-year-old father of two in Toronto, awoke to the alert and quickly made a hotel reservation more than 60 miles away in Niagara Falls.

“Having watched Chernobyl didn’t help,” he said, referring to the TV show about the 1986 nuclear disaster in the Soviet Union.

“The lack of communication following the alert didn’t help either,” he said.

“I have no problem leaving my phone on for these types of alerts,” mR Vlahos said. “But I would expect some more info from the government so I wouldn’t have to overreact the way I did.”

Many people slept through the first alert and saw it was a false alarm by the time they woke up.

Pickering mayor Dave Ryan said he was demanding a full investigation into the error.

“Like many of you, I was very troubled to have received that emergency alert this morning. While I am relieved that there was no actual emergency, I am upset that an error such as this occurred. I have spoken to the Province, and am demanding that a full investigation take place,” Mr Ryan said by Twitter.

Toronto mayor John Tory joined him, tweeting that “there are far too many unanswered questions” and noting it went out across the province of 14 million people.

“Last night may have been the wrong night to start watching Chernobyl,” tweeted CBC journalist David Common.

“It’s comforting to know that when the apocalypse does come, we’ll all still be snarking on Twitter,” Emmett Macfarlane, a University of Waterloo professor, tweeted.

The US Department of Homeland Security’s inspector general recommended changes to emergency alert system in the United States after Hawaii officials in 2018 mistakenly warned the public about a nonexistent incoming ballistic missile.

A Hawaii Emergency Management Agency employee sent the missile alert to mobile phones and broadcasters, triggering panic until the agency sent another message 38 minutes later notifying people it was a false alarm.

Pickering, opened in 1971, and had been scheduled to be decommissioned this year, but the province’s government committed to keeping it open until 2024. Decommissioning is now set to start in 2028.

It generates 14 per cent of Ontario’s electricity, and is responsible for 4,500 jobs across the region, according to Ontario Power.

It has experienced several earlier incidents. In 2011, a pump seal failure caused the spill of more than 19,200 gallons of demineralised water into Lake Ontario, although with no significant risks to public health, according to local authorities.

In 1994, the plant automatically shut down after a faulty valve caused 132 tons of heavy water to spill.

It was the first time a Canadian nuclear reactor had to use the emergency core cooling system to prevent fuel overheating.

Ontario Power “has a sophisticated and robust notification process in place that we would immediately follow in the unlikely event of an incident at the station,” said Chief Nuclear Officer Sean Granville.

“I want to assure the public that there was no incident at the station, and the plant is operating as designed.”