MUSKOGEE, Okla. (AP) — Officials say a fire and subsequent explosion at a Georgia-Pacific paper mill in eastern Oklahoma injured at least five people.

Muskogee County Emergency Medical Service operations director Ron Morris says four injured were taken to a hospital with smoke inhalation and undisclosed "minor trauma." A fifth person was treated at the scene.

Georgia-Pacific spokeswoman Karen Cole said two people were still hospitalized Tuesday.

The fire and explosion that followed occurred shortly before 10 p.m. Monday at the Georgia-Pacific plant in Muskogee, about 50 miles (80 kilometers) southeast of Tulsa.

Cole said firefighters were still trying to determine what caused the blaze and that reports that the fire began on a propane-fueled fork lift are unconfirmed.

Fire Chief Mike O'Dell did not immediately return a phone call for comment Tuesday.