An "operational incident" caused an explosion at BP's oil refinery in northwestern Indiana, the company confirmed in an emailed statement to the press on Thursday, but no one was injured.

One employee was taken to hospital, but later released, and the incident did not result in major disruption of production at the facility, BP added.

The refinery, located in Whiting, is BP's largest oil refinery in the U.S. and has a production capacity of 350,000 barrels per day, according to figures reported by Reuters.

An explosion in a processing unit caused the incident but was handled by the plant's fire department within a couple of hours, BP America spokesman Scott Dean told the Associated Press.

Dean said the company did not know what caused the explosion, or if it caused any chemical releases from the facility, which has a residential area on its western border.

A spokesman for the Indiana Department of Environmental Management was also unaware of any problems with air quality, resulting from the explosion and the following blaze.

A malfunction at BP's Whiting facility in March spilled about 1,600 gallons of oil into Lake Michigan, but the refinery covers 1,400 acres along the shoreline of the lake.