An explosion at a College Park paper plant early Wednesday caused heavy fire and forced some employees to flee the building, authorities said.

According to a media release by College Park fire officials, the Kapstone Paper Plant in the 2300 block of Sullivan Road suffered a boiler explosion, which caused two exterior walls to be blown out. Heavy fire resulted in the rear area of the building, as well as a large grass fire outside.

Also, a Fulton County hazardous materials unit was called out to determine if a 10,000 gallon diesel tank was leaking. No leak was found. About 20-30 workers in the building escaped without injury.

The cause of the explosion is being investigated by the fire marshal and Bureau of Alcohol, Tobacco, Firearms and Explosives officials.