MURDOCK, (AP) - A stretch of U.S. Highway 12 will remain closed after a collision between a Burlington Northern Santa Fe train and a semi carrying anhydrous ammonia injured four people, caused a leak of the chemical and evacuated an elementary school in western Minnesota.

Swift County sheriff's officials say the collision between the train engine and semi happened about 8:30 a.m. Tuesday west of Murdock.

Authorities say anhydrous ammonia continues to leak from the tanker. Residents within a 2-mile radius were asked to stay away.

The sheriff's office says the semi driver is in critical but stable condition in St. Cloud. BNSF spokeswoman Amy McBeth says three train crew members suffered non-life-threatening injuries.

Students from Murdock Elementary were moved to Kerkhoven High School. None of the cars of the train derailed.