LIMA TOWNSHIP, Wis. (AP) -- Authorities say a propane tanker truck has exploded and ignited several buildings at a farm cooperative in southern Wisconsin.

Rock County 911 supervisor Brian Becker says the explosion occurred Friday at a Cooperative Plus facility in Lima Township, near the city of Whitewater. He says several buildings are on fire.

The Rock County Sheriff's Office and Whitewater Fire Department are responding to the scene.

Becker says it's unclear what caused the explosion. He says there are no reports of injuries.

The Department of Labor issued $721,000 in penalties to Cooperative Plus after a worker was seriously injured at its Burlington facility in February 2010. They faced other penalties later that year for federal workplace safety violations at both its Whitewater and Genoa City sites.

(Copyright 2012 by The Associated Press. All Rights Reserved.)