(Reuters) – An explosion at Husky Energy’s refinery in Superior, Wisconsin, injured at least five people while sending smoke billowing into the sky and shaking a building a mile away, officials at the local fire department and a hospital said on Thursday.

Four people were being treated at nearby Essentia Health-St. Mary’s Medical Center and a fifth was on the way, said a hospital spokeswoman. She described their injuries as varied, but said she could not offer further details.

There were no immediate reports of fatalities.

“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.

Local media had earlier reported 20 people injured.

The company was responding to an incident at the refinery and emergency crews were on site, Husky spokesman Mel Duvall said, adding, “We are aware an individual has been transported to the hospital.”

Roads around the refinery have been blocked and employees evacuated, with several ambulances seen leaving the site, local media reported.

“It shook our store. Everyone was wondering what was going on. You could see the lights flickered, it knocked out one of our computers, it shook the ceiling,” said Tammie Carroll, an employee at Super One Foods in Superior, which is located about 135 miles (217 km) from Minneapolis, Minnesota.

The Superior school district, on its website, said it had been advised by police there was no need to evacuate.

Husky purchased the 38,000 barrel per day refinery from Calumet Specialty Products Partners LP last year.

Husky shares were down more than 3 percent at C$18.43 on the Toronto Stock Exchange the same day it reported financial results.

(Reporting by Vijaykumar Vedala and Arpan Varghese in Bengaluru and Stephanie Kelly in New York; Editing by Chizu Nomiyama and Scott Malone)