COPPELL, Texas -- Fire investigators are trying to find the cause of an overnight strip mall fire that affected three businesses.

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Video: Coppell Shopping Center Catches Fire

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Smoke damaged the Speedy-K convenience store, Ole's restaurant and the Lakeside Cleaners in the 600 block of East Sandy Lake Road, firefighters said.

Firefighters said the smoke was so heavy when they arrived at about 3 a.m. that they had a hard time finding the fire, but limited fire damage to the convenience store. Investigators said they think the fire started behind a cooler in the convenience store.

"They were able to cut it off to the origin of the business," Chief Kevin Richardson said.

Investigators said all the businesses in the strip center sustained smoke and water damage.

Thirty-five firefighters from four units assisted, firefighters said.