The city's fire chief says overheated brakes were the suspected cause of the blaze night blaze in the middle of the busy parking lot. The driver said he pulled over when he smelled smoke from the back of the truck.
The Portland Press Herald reports that nobody was injured in the fire.
The driver was on his way from the Canadian province of Prince Edward Island to New Jersey to deliver the fries. Waterville is about 15 miles north of Maine's capital, Augusta.
The truck is operated by Midland Transport, a Dieppe, New Brunswick-based company.