– Millions of people in Ontario, Canada's most populous province, were greeted by a screeching alarm on their cellphones Sunday morning and an ambiguous "emergency alert" about an "incident" at one of the world's largest nuclear power plants.

But after about 90 minutes of puzzling by Canadians over a possible nuclear Armageddon, the warbling siren sounded out again from phones across the province with another alert taking it all back.

"The previous alert was issued in error," the second message read. "There is no danger to the public or the environment."

Latest embarrassment

The false alarm over a possible emergency at the Pickering Nuclear Generating Station, which sits on the shore of Lake Ontario to the east of Toronto, is the latest embarrassment for Canada's national emergency alert system, which was expanded to phone from broadcast warnings just over 1½ years ago.

The warning in Ontario didn't set off a panic, unlike an erroneous message about a ballistic missile threat in Hawaii in January 2018. But it did appear to add to public frustration about a system that some people have criticized for crying wolf or for creating needless disturbances.

On social media, a number of people reacted with good humor. "This is embarrassing because I had JUST finished organizing my neighborhood into a band of foraging mutants," Jonathan Kay, a journalist in Toronto, tweeted with the first warning attached.

Neither the office of Ontario's Solicitor General, which is responsible for the province's emergency alert system, nor Ontario Power Generation, the government agency that owns Pickering's six operation reactors, responded to questions about where or how the error had been made.

But Isabelle Roy, a spokeswoman for the Canadian Nuclear Safety Commission, confirmed that there was no safety risk at the power station.

The alert appeared to have been sent throughout the sprawling province, which spans parts of two time zones. But exactly how many people were startled out of bed or over breakfast is unclear.

While the alarm overrides any silencing of phones, it cannot switch on handsets that have been shut off. Nor does it work with phones that are connected to older cellular networks that are sometimes the only service in remote areas.

Most messages sent by the system are Amber Alerts, usually involving children who have been taken by one of their parents in contravention of a court order. But it can be used to issue alerts about dangerous weather, particularly tornadoes, or other potential emergencies.

The federally mandated alert system has struggled with technical problems that resulted in early test messages failing to reach large numbers of phones.