Superior schools Superintendent Janna Stevens said late Thursday afternoon that all students were either home safe with their families or were on their way home. Residents were still encouraged to remain away from their homes for another two hours.
Later Thursday, a massive plume of smoke began billowing from the refinery. "But stay tight" until further notice, Superior Mayor Jim Paine said.
Residents who evacuated and needed shelter gathered at the Duluth Entertainment Convention Center as the primary site.
Friday classes were canceled in Superior and nearby Maple school districts. The non-regulatory federal agency investigates serious chemical accidents such as refinery fires.More news: Alfie Evans: parents will ask doctors to take their son home
Burning asphalt at the Husky Energy refinery in Superior, Wisconsin, has prompted the evacuation of much of the town of about 27,000. Cheryl Thielman, 58, who manages a mobile home park near the refinery, told AFP that the explosion was a "huge boom".
At least 20 people were injured in an explosion and fire Thursday morning at the Husky Energy oil refinery in Superior, Wis.
It was unclear how many people were being evacuated. The corridor downwind to the south of the refinery is sparsely populated.
The number of people injured in a refinery explosion in Wisconsin has grown to at least 11.More news: Kanye West Posts Private Plea from John Legend to Dump Trump
"So initially it was on standby then several additional emergency room physicians came in, but we also had additional critical care, trauma, surgeons, hospitalists and other staff available", said Essentia Health Hospitalist Dawn Drotar. She says the extent of injuries is unknown.
In Duluth, St. Luke's Hospital was treating one person and did not expect to receive any more, spokeswoman Jessica Stauber said.
Specialists from Williams Fire & Hazard Control of Port Arthur, Texas were hired by Husky Energy and were flying to the scene on Thursday to direct efforts to battle the blaze. Superior Fire Chief Steve Panger has said there are no known fatalities. Superior police later tweeted that the fire had reignited and urged residents living within the evacuation area to leave.
Authorities now say five people have been taken to hospitals after an explosion rocked a large refinery in Wisconsin. The smoke was visible for miles, seen in this video from the Great Lakes Aquarium in Duluth, Minnesota, across Superior Bay from the refinery.More news: Princess Charlotte's floral dress sells out within 24 hours