Students at Chilliwack secondary school were confined to their classrooms Thursday afternoon as police descended on the school to investigate a threat.

"A message was located in the school. It indicated a veiled non-specific threat," RCMP spokesperson Cpl. Tammy Hollingsworth said.

The threat came just hours after the school had held a routine lockdown practice drill in the morning.

Police responded, but both Mounties and school officials stressed the school was never in lockdown.

"Lockdown procedures occur when we have an active shooter scenario," Hollingsworth explained. "What we were doing was a hold-and-secure."

She described a hold-and-secure, in which students were kept in their rooms as officers investigated, as occurring when "There's been some sort of indication there's been a potential threat to the students."

Students were released, as scheduled, at 2: 45 p.m. They were given letters to give to parents.

The letter was signed by principal Rick Jones and said, in part:

"There was a highly visible police presence and the police are taking precautions at this point. There is no reason to believe that our students and staff are at risk or there is jeopardy to anyone's safety."