April 26 (Reuters) - An explosion at Husky Energy's refinery in Superior, Wisconsin, injured at least 10 people, sent smoke billowing into the sky and shook a building a mile away, officials at the local hospitals and the fire department said on Thursday.
At least 10 people were taken to local hospitals, one of whom was seriously injured, said a spokeswoman for Essentia Health-St. Mary's Medical Center, which operates hospitals in Superior and nearby Duluth, Minnesota. The other nine injuries are not life-threatening, she said.
It was unclear what caused the explosion, Husky Energy spokesman Mel Duvall said.
There were no immediate reports of fatalities, and Duvall said all of the refinery's workers had been accounted for. The facility can process up to 38,000 barrels of oil a day.
"The whole building shook. The lights flickered three times and the whole building shook," Jim Ronning, owner of Hudy's Tavern in Superior, located about a mile (1.6 km) from the facility.
A spokeswoman for St. Luke's, which operates two hospitals in the area, said it was treating one injured patient, but did not provide details on that person's condition.
The local Fox affiliate said more smoke appeared after 1 p.m. EST (1700 GMT), after receding from the initial explosion.
Roads around the refinery were blocked and employees evacuated, with several ambulances seen leaving the site, local media reported.
"You can still smell a real caustic smell in the air," said Sara Haugen, owner of Pudge's in Superior, located about 135 miles (217 km) from Minneapolis, Minnesota. "There's a big black plume of smoke coming out."
Husky purchased the refinery from Calumet Specialty Products Partners LP last year. It produces asphalt, gasoline, diesel and heavy fuel oils, largely using heavy crude oil imported from Canada.
Husky shares were down more than 3 percent at C$18.46 on the Toronto Stock Exchange the same day it reported financial results. (Reporting by Vijaykumar Vedala and Arpan Varghese in Bengaluru, Stephanie Kelly in New York and Erwin Seba in Houston Editing by Chizu Nomiyama and Scott Malone)