Oops.

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

The message, which was transmitted throughout the nation’s most populous province, was accompanied by a shrill emergency broadcast noise. It said an unspecified event had occurred at the Pickering Nuclear Generating Station. There was no abnormal release of radioactivity, it added, and people did not need to take protective action.

More than an hour later, utility officials sent another message saying the alert “was sent in error” and that there was “no danger to the public or environment.”

“No further action is required,” said the message, which was also sent to television screens.