UPDATED 12/12/11 3:20 p.m.

SKOKIE, Ill. (CBS) — A two-story apartment building exploded in north suburban Skokie on Monday morning, sending flames shooting high into the air and leaving a man injured.

The apartment structure at 8734 N. Kimball Ave. was almost completely destroyed in the blast. The front wall of the building and most of the roof were blown out by the explosion.

One man was injured, CBS 2’s Vince Gerasole reports. The building, undergoing renovations, wasn’t occupied at the time of the explosion, but authorities say a relative of the owner was approaching the structure at the time of the explosion.

He was seriously injured and taken to a nearby hospital.

Residents in the buildings on either side were evacuated as a precaution.

“My grandbaby was scared, completely jumped in my arms after the explosion I looked out the window to see what had happened and we saw the fire,” next-door neighbor Minnie Pierce said. “I said, ‘We need to go.’”

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By 11 a.m., only a shell of the building was left, with just two side walls holding up the roof. Fire crews could not go in, the stability of the structure was in question, and what remained of the building seemed to be on the brink of collapsing.

The building’s integrity was so damaged — with cracks and buckles on the remaining walls — that crews could only examine the structure from afar. The view from a fire ladder was as close as they could get to survey the damage.

Fire crews arrived around 9:30 a.m.

“When crews arrived on the scene, the building was fully involved at the time, and the whole front of the building had already collapsed,” said Skokie Deputy Fire Chief Jim Walters.

The residence is just south of a commercial strip on Dempster Street.

Danny Hechtman, co-owner of Ken’s Diner, 3343 Dempster St., was just down the street from the blast.

Hechtman said there was a huge fire, with flames shooting 30 feet above the roof.

“The building was fully engulfed by the time I came out of the restaurant,’ he said. “It was really an incredible scene.”

Other witnesses described a shocking and terrifying scene.

“All of a sudden I heard this, ‘Boom!’ and I looked at the side of the house, and the side of the house was cracking,” said witness Katie Thomas, “and all of a sudden I looked up and I saw this big old black smoke, and I got out of the car. I panicked. I thought it was out of their building, and then all of a sudden the front – there was so much fire coming out of the front.”

The gas was shut off to the damaged building, and Nicor gas crews were digging near the scene.

Dempster Street was closed after the explosion, but had reopened by 11 a.m., CBS 2’s Kris Habermehl reports. But an Illinois Department of Transportation salt truck was parked in the right lane to keep traffic away from Kimball Avenue.

Kimball Avenue itself was expected to remain closed south of Dempster Street as long as crews remain on the scene, and concerns about a collapse persist.

Complicating the traffic situation, two cars slammed into each other in a head-on collision a mile away at McCormick Boulevard and Oakton Street about a mile away. That forced some of the fire companies that had been assigned to the Kimball Avenue explosion to the accident scene.