CHICAGO (CBS) — A man was killed early Thursday in a house fire in northwest suburban Hoffman Estates.

The fire started around 1 a.m. at a home in the 600 block of Mohave Street. A neighbor called 911 after spotting flames at the rear of the home.

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“A slight boom, and my house shook several times. So, something happened. Obviously, it had to do with the fire. What, I’m not sure,” neighbor John Mazeikis said.

Firefighters said they were not aware of any type of explosion, and as of late Thursday morning were still investigating the cause of the fire.

More than 40 firefighters from Hoffman Estates and other nearby towns responded, and found a man believed to be in his 60s in one of the back rooms.

The man was taken to the hospital, where he later was pronounced dead.

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Firefighters said there was a large amount of fire in the house.

“A fairly good sized fire; heavy amount of fire damage, smoke damage throughout the home. First arriving companies did report that there was a smoke detector working in the home. They could hear the smoke detector, the audible smoke detector, as they entered the home,” Hoffman Estates Fire Department Battalion Chief Patrick Fortunato said.

Denise Claxton lost her neighbor of 17 years.

“It’s kind of unbelievable, that’s all I can say. You don’t expect it, especially now in this time of year,” she said.

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Neighbors said the man who died leaves behind a son and daughter, and some grandchildren.