LENOIR, N.C. – Classes at a Caldwell County school were canceled for cleaning Thursday after four students were exposed to mercury.

The incident happened Wednesday morning at Whitnel Elementary School in Lenoir.

School district officials say a student brought suspected mercury into the school in a vial and it broke inside the classroom. The four affected students were treated and released at a nearby hospital for suspected mercury contamination.

The school was evacuated and students were taken to a nearby church.

The Environmental Protection Agency said it plans to work around the clock to clean the building.