A young boy has been airlifted to a Toronto trauma centre after being struck by a falling tree branch at a school in south Oshawa on Thursday afternoon.

Durham Regional Police say emergency crews were called around 12:10 p.m. to Monsignor Philip Coffey Catholic School, where a boy under 12 was underneath a large tree when a limb fell and struck him in the upper body. He was trapped for a time and initially believed to be without vital signs before responders began life-saving efforts and later found signs of life.

Officials said it took multiple responders to remove the branch from the child before he was transported by Ornge air ambulance to hospital for further treatment.

The incident occurred during lunch recess, according to the Durham Catholic District School Board, which said it is supporting students and staff while working with emergency services.

Police are investigating the cause of the branch failure, with weather conditions and possible tree maintenance issues among the factors being examined.