LAKE FOREST, Ill. (CBS) — An extra alarm fire totaled a north suburban mansion overnight, causing an estimated $3 million to $4 million in damage.

Lake Forest Fire Department Deputy Chief Kevin Issel said a homeowner called 911 shortly before midnight to report his two-story house on fire at 1150 W. Keswick Ln.

The battalion chief was the first to arrive on the scene and Deputy Chief Issel said, even by then, the “large home was fully involved in fire.”

Issel said the roof of the house was starting to collapse when the first fire engine arrived within 4-5 minutes of being called.

He estimated the house was 6,000 to 7,000 square feet. Only the walls were left standing.

The Lake Forest Police and Fire Departments were investigating the cause of the fire. Issel said, because of the extent of the damage, it’s unclear where or how the fire began.

Issel said the two homeowners escaped without injury. No firefighters were hurt, either.

Approximately a dozen other fire departments helped Lake Forest firefighters extinguish the blaze.

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