Environment Canada is trying to determine whether a tornado was responsible for ripping the roof off an elementary school in Hamilton, Ont., on Wednesday, slightly injuring two students.

The children were among a group practising volleyball in the gym of the Lawfield Public School at about 4 p.m. when a bout of severe weather hit.

"I just heard a big gust of wind and the roof just collapsed," said Matt Theoret, one of the students in the gym. "The windows blew in... We all ran."