CHICKASHA, Okla. (AP) - Firefighters in Oklahoma are battling a fire on an oil rig.

Authorities say the oil rig is about 6 miles east of Chickasha. Video of Wednesday's blaze showed a large plume of thick black smoke rising from the rig.

The Oklahoma Department of Transportation says nearby roads are closed because of the smoke. Department spokesman Cody Boyd says the road may remain closed for several hours.

The owner of the site, Continental Resources, said all employees have been accounted for and are safe and that the cause of the fire is unknown.

Chickasha is about 45 miles southwest of Oklahoma City.