About two dozen homes have been evacuated and two firefighters taken to the hospital after toxic fumes were released from a chemical spill on a highway in southern Virginia.

Danville city spokesman Arnold Hendrix says the smoking packages of magnesium phosphide were reported around 11:40 a.m. The product is used to fumigate local tobacco warehouses for rodent control.

Magnesium phosphide reacts with water, so rain caused several of the containers to release the toxic gas.

Two firefighters who were exposed to the fumes were transported to the hospital as a precaution.

A shelter was opened at a nearby recreation center for evacuated residents. Students at Glenwood Elementary School, just outside the evacuation area, were kept inside but continued classes.