SUPERIOR, Wis. -- 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," FOX News reported.
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, FOX News reported.
This story is developing.