SUPERIOR, Wis. (Fox News) – At least 20 people were reportedly injured at an oil refinery in Wisconsin on Thursday after a sudden explosion that witnesses said rattled the air like a “sonic boom.”
The explosion broke out at Husky Energy oil refinery in Superior, Wis., the Milwaukee Journal-Sentinel reported.
The Superior Police Department tweeted civilians should stay away from the area due to a “large incident.” WDIO reported workers were being evacuated from the building. Police have not asked nearby residents to leave their homes.
Local reports said six people had been transported to a hospital and there appeared to be no deaths. Officials said the explosion may have been caused by an asphalt leak and the scene is now contained and controlled. The fire is said to be out.
The Superior School District announced that “at this time, there is no reason to evacuate any of the school buildings. We will be keeping all students in the buildings.”
Witnesses told KQDS the explosion could be felt from a few blocks away. Large clouds of smoke were seen coming from the refinery.
A contractor who was inside the building told WDIO television that the explosion sounded like “a sonic boom” that happened when crews were working on shutting the plant down for repairs.
The refinery, the only one in Wisconsin, has about 180 employees.
The Associated Press contributed to his report.