An evacuation at Northern Secondary School has now ended after classes were cancelled Friday morning while police investigated a threat against the school at Mt. Pleasant Road and Roehampton Avenue..

"Police have concluded the search of our school and have indicated that it is safe for return," principal Ron Felsen wrote in an email to CBC News.

"This has been a challenging day for us as we worked through this situation. As you can appreciate, relocating a school of 2,000 and then canceling classes is no simple matter," Felsen said.

Police told CBC News Friday afternoon that the bomb squad had been involved in the search, but their investigation turned up nothing. Because of the nature of the call, they said, they were unable to say more about how the threat was received.

As administrators worked to contact parents about the evacuation on Friday morning, many students were sent to North Toronto Collegiate Institute, located several blocks west at Broadway Avenue and Yonge Street, just north of Eglinton Avenue.

All students and staff are safe, Feslen said at the time, urging students to continue working on their courses from home where possible.

"We never want to disrupt the school day but we always want to take every precaution to ensure the safety of our students and staff," Felsen wrote in an email on Friday afternoon.

The school's student council elections were postponed until Tuesday morning, according to Felsen's note. It would "seek clarification" on rescheduling an exam.

In an earlier email to parents, Felsen said that a threat was made against the school "early this morning" and officers were searching the building and the grounds.

Canine officers and their dogs could be seen outside the school Friday morning. Police said they received a call around 6:05 a.m., but at the time neither they nor a TDSB spokesperson could confirm the nature of the threat.

Portions of Mount Pleasant Road, Rawlinson Avenue and Broadway Avenue were closed as police investigated but have since reopened.

Northern Secondary evacuated as safety precaution for <a href="https://twitter.com/TorontoPolice">@torontopolice</a> investigation. Students/staff safe + redirected to North Toronto CI. —@tdsb