Video (01:33) : An explosion rocked a large refinery in Wisconsin Thursday, injuring several people, a fire official said.

UPDATE: The evacuation order for Superior, Wis., has been lifted as of 6 a.m., the city's mayor announced in a Facebook post Friday morning.

"All indications are that the refinery site is safe and stable and the air quality is clean and normal," Mayor Jim Paine wrote in a 5:38 a.m. Facebook post.

"I am lifting the evacuation order at 6 am this morning...," he wrote. "Welcome home."

The police department followed the mayor's announcement with a tweet shortly before 6:30 a.m., saying "As of 6am today, the evacuation order has been lifted, and you may return to your home."

A spokesperson for Husky Energy said the fire is out but that hot spots are being monitored.

It’s raining lightly in Superior, which may have helped boost confidence that the fire was finally over and that the danger had passed.

Map: Husky Energy oil refinery, Superior, Wisconsin Map: Husky Energy oil refinery, Superior, Wisconsin

The atrium at Superior’s government center building was empty Friday morning. Gone were the various media who had camped out inside late into Thursday night, along with the podium that had stood ready for what had been a series of press conferences as the fire burned.

On Thursday night, police officials had said there would be a press conference at 10 a.m. Friday. It's unclear if that press conference will still be held.

The evacuation order has been lifted, but the Superior Police Department has some roads near the refinery blocked to everyone except those investigating the fire. It wasn’t immediately clear Friday morning when those roads would reopen.

This is a breaking news update. Original story is below. Check back for more updates.

– A massive oil refinery fire that burned for hours and threatened to rage out of control in this Twin Ports city was beaten down by firefighters Thursday night after noxious fumes forced a widespread mandatory evacuation of residents.

A giant plume of oily, black smoke from burning asphalt spread for miles and for hours after a series of explosions ripped through the Husky Energy refinery Thursday morning, sending 11 people to the hospital and leading officials to order the evacuation of more than 70 square miles around the facility, including three schools and a hospital. No deaths were reported.

Officials have yet to determine the cause of the initial explosion.

Kollin Schade, a Husky Energy spokesman, said the blast occurred in the fluidized catalytic cracking area of the refinery. That’s a part of the refining process when crude oil is subjected to heat and pressure to extract gasoline and other light petroleum products.

The company won’t speculate on the cause until after an investigation, Schade added.

After more than eight hours of fear and uncertainty, the fire was knocked down.

Just before 7 p.m., Mayor Jim Paine gave the 27,000 residents of Superior good news. “Breathe easy,” he said. “This fire is out.”

But about 2½ hours later, Superior police reported that a secondary fire had started “due to the ongoing high heat at the scene.”

It, too, was knocked down, Paine said late Thursday, but the evacuation was to remain in effect into the night, with hourly reassessments.

The day of drama began shortly after 10 a.m., when the first in a series of explosions ripped through the refinery in the Lake Superior town, which shares a harbor with Duluth.

By Thursday afternoon, the ensuing fire was burning so intensely that firefighters said they couldn’t attempt to put it out.

“We can’t get people close enough to actually put the fire out,” said Scott Gordon, a battalion chief with the Fire Department.

Gallery: Superior, Wis. refinery explosion Gallery: Superior, Wis. refinery explosion

Gordon said the danger to firefighters was not only from the blaze, but also from other chemicals and petroleum products that could ignite.

But as the afternoon wore on, a crew of about 30 firefighters got “enough water and enough water pressure” on the fire to extinguish it, Gordon said.

Later, the secondary fire was reported, but it, too, was knocked down by firefighters, this time with the use of foam fire retardant.

Officials said the evacuation, which affected several thousand people, was a precaution. “Better safe than sorry,” said Paine, calling the explosion and fire “a nightmare scenario.”

Soon after the first explosion, officials thought the fire was under control. But after a second series of explosions and a growing smoke plume, authorities began evacuating the area for miles around.

About 2 p.m., Essentia Health St. Mary’s Hospital in Superior shut down, closing its emergency room and transferring all patients to Essentia Health St. Mary’s Medical Center and Benedictine Health System, both in Duluth.

Three schools included in the evacuation zone — Great Lakes Elementary, Superior Middle School and Northern Lights Elementary — bused children to the Amsoil Facility parking lot at 1011 Susquehanna Av., Superior police reported.

The Duluth Transit Authority diverted buses from regular routes for the evacuation, and Duluth city officials opened the Duluth Entertainment Convention Center for Superior evacuees.

Natalia Johnson, 12, right, and her sister Iley, 15, stood outside Amsoil Arena in Duluth with their 6-year old pug, Tucker, and some of their belongings following the evacuation of Superior, Wis., on Thursday.

By midafternoon, around the time officials said the blaze was too hot to fight, the National Weather Service said the smoke plume had reached beyond Solon Springs, about 30 miles southeast of the refinery, and appeared as a storm cloud on radar.

The initial blast shook a nearby golf course, rattled offices in Superior’s business district and sent thick, black smoke into the sky above the refinery.

“We had a huge boom, and it came through and rattled the whole clubhouse,” said Allie Fuller, assistant operations manager at Nemadji Golf Course about half a mile south of the refinery. She said golfers on the course “got really scared,” but no one was injured. After the fire reignited around noon, the golf course was evacuated.

Superior resident Sadie Johnson, who was among evacuees congregated Thursday night at the convention center, said she received several voice mails and texts signaling evacuation of the schools attended by her five children, ages 9 to 14. She said the mood was calm when she went to the Amsoil Facility lot to pick them up. “It wasn’t a riot atmosphere,” she said.

Her daughter Natalia, 12, said she was in class at Superior Middle School when her teacher went to look out the window and said to herself, “That’s big.” The students flocked to the window to see for themselves. Shortly afterward, the school was evacuated.

Taylor Pedersen, president and CEO of the Superior-Douglas County Chamber of Commerce, said he heard the first explosion from his office, located near the University of Wisconsin-Superior, about a mile from the refinery.

“There was one large boom,” he said. “We’re just trying to figure out what exactly happened, and of course keeping everyone involved in our prayers.”

A four-person team from the U.S. Chemical Safety Board headed to Superior Thursday afternoon to investigate. The board makes safety recommendations after serious chemical incidents.

Thick smoke pours from the fire at the Husky Energy oil refinery in Superior, Wis., on Thursday afternoon.

About 180 people work at the refinery, which was closed for cleaning at the time of the initial explosion. A spokeswoman for Paine said some of the injured may be employees of the cleaning vendor.

The refinery, built in 1950, was owned for decades by Murphy Oil, which bought it in 1958. Murphy sold it to Calumet Specialty Products in 2011 for $435 million, and Calumet sold it to Calgary-based Husky last year for $492 million.

In 2015, when Calumet was owner, OSHA issued four citations to the refinery, three of them for serious violations. They involved flammable and combustible liquids and hazardous waste operations and emergency response. Calumet was fined $21,000 but negotiated a settlement of $16,800.

The refinery is small, producing about 38,000 barrels per day. That’s about 10 percent of what Flint Hills’ large refinery in Rosemount produces, and less than 40 percent of the production at Andeavor’s refinery in St. Paul Park.

The Superior refinery produces gasoline, diesel fuel, motor oils and asphalt, primarily for local markets, according to the U.S. Energy Information Administration.

Staff writer Mike Hughlett contributed to this report.