UPDATE: New information can be found in our story about the damage assessment and cleanup.

CANTON — A natural-gas explosion Wednesday night in downtown Canton killed one person, authorities said.

The deceased was an Ameren Illinois employee, part of a crew that was investigating a gas leak in a building at 45 East Side Square. Ameren and Graham Hospital officials did not identify the worker.

At least 11 others required hospital attention.

The explosion took place shortly before 6 p.m. The Ameren workers arrived about 5:30 following a report a contractor damaged a gas-service line, according to utility spokesman Tucker Kennedy.

“The utility business is a close brotherhood, and our family is hurting right now,” Kennedy said about 10 p.m. during a news conference at the hospital.

“We express our deep sadness and our profound sympathies to the family of our fallen Ameren Illinois worker and ask everyone to keep their family and our family in their thoughts and prayers.”

The crew had shut the line and was making repairs when the explosion took place, according to Kennedy.

“It’s an unfortunate and tragic accident,” Canton Mayor Jeff Fritz said.

Jill Dillefeld, of Canton, a psychiatric nurse, said she was eating at Billy's Tap, about a block from the square, when she heard a boom.

"All of the sudden, I heard the biggest kaboom I have ever heard in my life," she said. "I thought, 'Oh my God, it's lightning,' but then I realized it wasn't storming.

"Everyone jumped. The door where I was sitting blew open."

The power flickered off and on and then people rushed outside, looked to the square and saw smoke.

"My nurse instincts kicked in. I ran down and saw a man lying in the parking lot near Dollar General," Dillefeld said. "He had been there working on a gas leak that they were called to work on. He reminded me of those 9/11 victims that you saw, all covered with dust and debris."

The man was alert but wanted to know about his co-workers. Another man emerged from the rubble. He had a big knot on his forehead. She looked up and saw a third man, buried in the rubble. She stayed with the first man until paramedics arrived and then tried to help the other injured man. But she was shooed away from first responders. As she walked off, she saw a fourth person, a bleeding man who had been struck on the head with tile from the building's ceiling where he was when the explosion happened. A beam from the building, he told her, hit his leg.

"He was just there on the curb of the sidewalk. Bless his heart, he kept telling me that he was OK, that he just had a small bruise on his leg, but I could tell he was in shock. He was so cold," she said.

The building where the explosion occurred was known as the Opera House Professional Center. It dated from the 1890s, according to a website about Illinois theaters. Currently the building housed offices, including that of the Canton Area Chamber of Commerce.

Officials could not confirm how much damage was done to that structure. In the overall area, damage was extensive, according to Canton Police Chief Rick Nichols. Broken glass was strewn around downtown streets.

Thoroughfares in a two-block radius were closed, with entry prohibited except for authorized personnel.

The Salvation Army office in Canton was available as lodging for area residents unable to return home.

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— Nick Vlahos (@VlahosNick)November 17, 2016

Between 6 p.m. and 10 p.m., Graham treated and released seven patients, according to Bob Senneff, the hospital president and CEO. The hospital admitted three patients. Another was transferred to OSF Saint Francis Medical Center in Peoria.

Senneff did not have condition reports.

At 7 p.m., Ameren Illinois reported more than 500 power outages in the Canton area, Kennedy said. All were expected to be resolved by midnight.

The explosion was among several natural disasters that have affected downtown Canton over the years.

In 1975, a tornado struck the area. In ensuing years, fires destroyed buildings along or near the square.

Following the most recent devastation, downtown was filled with police, firefighters, emergency-service crews and onlookers.

Richard Meyer, an optician at Bard Optical, 127 N. Main St., was working at the time of the blast.

“The lights went out, I heard a big boom and I felt pressure,” said Meyer, a Cuba resident. “The next thing you know, all the glass was broken. I didn’t smell anything.”

The Bard office manager, Jessica Boughan, was on her supper break at a restaurant and bar down the block.

“We thought someone drove into the side of the building,” she said.

Bill Babb resides in a high-rise apartment building about three blocks north of the explosion site. He was watching television with his wife when an exterior flash illuminated his apartment.

“I was in the military 10 years in field artillery,” Babb said. “It reminded me of a 200-pound round coming down within a half-mile of me.

“My first impression was it was a gas explosion. It was too loud for just a transformer.”

Krysten Stremmel, 23, was watching TV at her house when she heard the explosion.

"Our windows shook," she said. "It sounded like a firework going off right in front of our house."

She and others got into their truck, drove five blocks or so to downtown and were stunned to find the damage.

"We walked through the strip of a mall that is left, between the Penney's, the H&R Block and the Taco Bell. All those windows were completely shattered," she said. Paper, she said, littered the ground. Clothes were all over the floor in the J.C. Penney.

She said there was a heavy smell of gas in the area.

BJ McCullum of Canton was at the high school, about a mile north of downtown, when the explosion occurred. He said it shook the basketball nets inside the gym. He lives south of downtown, and drove past the downtown on his way home. People were out everywhere, he said. He said he didn't smell gas, however.

Karen Calhoun was teaching a dance class at the Canton YWCA, which is just off the square in downtown, at time of the explosion.

"The power went out, the whole building actually shook. The sound was deafening, and I actually fell over from the shake," she said. "I have never experienced anything like it in my life. I dismissed my students to go home to safety as soon as we found out what happened a few minutes later."

When she stepped outside, she saw debris everywhere.

"When I stepped outside I saw debris floating, making the air cloudy. The stench of gas was awful and made my eyes water. I saw windows in neighboring buildings blown out with the glass in the streets and sidewalks," she said. "I went and saw bricks and all kinds of building materials spread all over the square."

Along Elm Street stood Rob Bobell, an optometrist who operates Progressive Vision Center, 42 N. Main St. About 90 minutes after the blast, Bobell was carrying a broom and shovel in an effort to clear broken glass from the street. But a police officer asked him to stay clear of the area.

“I thought maybe it was an earthquake,” Bobell said. “There was just lots of confusion at the time. I’m still in a daze, honestly.”

Bobell wasn’t sure if his building was damaged.

“I’m more worried about possible fatalities,” he said. “That’s my biggest concern right now. I’m not really worried about my building. I’m worried about that.”

Nick Vlahos can be reached at 686-3285 or nvlahos@pjstar.com. Follow him on Twitter @VlahosNick.

Andy Kravetz can be reached at 686-3283 and akravetz@pjstar.com. Follow him on Twitter @andykravetz.