WAUKEGAN, Ill. – An explosion ripped through a shopping plaza Thursday in a Chicago suburb, sending five people to a hospital, but none with life-threatening injuries, fire officials said.

The explosion struck around lunchtime in the business district, located about 40 miles north of Chicago.

The impact shattered windows and collapsed the roof of the plaza, which housed businesses including a cell phone shop, a tuxedo store and a hair salon.

Deputy Fire Chief Dan Young said authorities believe the incident was caused by a gas explosion and that some shop owners in the area had smelled gas for the last couple of days.

Officials were “99.99 percent” sure the rubble had been cleared, and there was no reason to believe anyone was missing, Young said.

“The whole back of the building was pancaked,” Young said.

Eight people were injured in the blast, and three were treated at the scene, Young said.

Of the five people sent to an area hospital, four were discharged by Thursday evening and one had been admitted, according to a hospital spokesman who said he did not know the remaining patient’s condition.

A fire that erupted had been extinguished, officials said, and Young said the injuries included smoke inhalation, bumps and bruises.

Candi Rixie said she was taking orders at Leno’s Submarine Shop, one block away from the shopping plaza, when she felt a huge tremor.

“We felt like an earthquake, like somebody had hit the building with a car,” she said.

Rixie said she ran out of the restaurant to see what had happened.

She and others said they first thought they saw bodies in the street, but quickly realized it was clothes and mannequins that had been on display in a store and blown outside by the blast.

Gary Podyma was taking inventory at the Living Foods Pantry health food store across the street from the shopping building when he heard a loud explosion and his windows blew out.

Then he saw a big, brown cloud and debris coming toward him.

“To see a building coming toward you like that – words can’t describe the feeling you get,” he said. “It was frightening, it was ominous.”

He said he also smelled a strong odor of gas immediately after the blast.

“It’s amazing that anybody survived,” he said.

People’s Gas spokeswoman Bonnie Johnson said a crew is on the scene but hasn’t been able to get close enough to say what might have caused the explosion because the fire department hasn’t given clearance.

“Until they give us a go ahead, there’s no way we can go in and investigate it,” she said.

David Motley, a spokesman for the city of Waukegan, said the brick building was decades-old.

“The roof blew up and off and fell back down,” he said.

Officials planned to bring in special equipment to dismantle the rubble on Friday, Young said.

Special equipment was needed because the building was unstable.

He said the U.S. Bureau of Alcohol, Tobacco and Firearms planned to assist in the investigation.

George Sanchez, general manager of Chicago-based Mena Travel agency, said his company’s Waukegan branch was adjacent to the explosion and employees inside felt the vibrations.

But the store wasn’t damaged by the blast.

“Our folks are OK. They were asked to vacate the premises for safety reasons,” he said.