MINNESOTA ? Nearly 40 students were injured Wednesday by a chlorine gas leak in the pool area of a high school where a shooting more than four years ago killed two boys, officials said.

Thirty-six students and a gym teacher were taken to hospitals from Rocori High School in Cold Spring, Mayor Doug Schmitz said. At least one other person was injured.

Twelve students and the teacher were admitted to St. Cloud Hospital to be monitored overnight, hospital spokeswoman Jeanine Nistler said. None was seriously ill, she said.

The leak was discovered before 2 p.m., and the building was evacuated, said Stearns County Chief Sheriff’s Deputy Bruce Bechtold. The leak was contained within an hour, he said. The cause was being investigated.