Some 60 schools and universities in eastern Canada were evacuated Wednesday over a series of bomb threats, including one received by police, that appeared to have been bogus.
No bombs were found, but administrators said the schools would remain closed throughout the day as police conducted another sweep of the schools, with classes expected to resume in the morning.
Authorities said they are investigating possible links between the threats, as well as to another that targeted at least one school in the United States.
"At this point, we don't know who is responsible for the threats," Royal Canadian Mounted Police Sergeant Kevin Bailey told a press conference.
He said the threats were received by fax machine. "The threat said there was a bomb in a school or a number of schools that would detonate today," Bailey said.
So far, searches had uncovered nothing suspicious, he said. "If nothing is found, I'll be satisfied that the threat was a hoax."
Earlier, the RCMP announced in a statement that all Prince Edward Island schools were being evacuated "due to a potential threat."
Students at all primary and secondary schools across the Atlantic island province were taken to designated safe locations, federal police said, with parents anxiously awaiting information about where to pick up their children.
In Nova Scotia, meanwhile, police were probing an anonymous bomb threat against three university campuses in the province.
The campuses of Nova Scotia Community College in Halifax and in Sydney were shuttered after local police received the threat, at about 7:50 am local time (1050 GMT).
Cape Breton University was also evacuated.
The US school or schools possibly also targeted were not identified by Canadian authorities.