Chicago, Apr 27 (IANS): An explosion broke out at an oil refinery in the US state of Wisconsin on Thursday, which resulted in at least multiple casualties, the media reported.

The explosion was reported at 10.06 a.m. at the Husky Refinery, which is the former Calumet oil refinery, Xinhua reported.

Authorities in Superior described the situation as an "evolving scene" in a news release. An initial news release from the Superior Fire Department reported at least 20 "casualties," but an updated release from Fire Chief Steve Panger said "at least 6 transported - no report on severity of injuries."

Panger said the fire was out by 11.20 a.m., although smoke could be seen rising from the plant. Panger said a small tank exploded containing either crude oil or asphalt.

Superior police are advising people to stay away from the area and roads around the refinery have been blocked off. There have been no neighbourhood evacuations.

Superior is a city of about 27,000 people that borders Minnesota to the north and the tip of Lake Superior.

According to local media, about 180 people work at the refinery, which provides the area with gasoline, asphalt and other specialty petroleum products.