ATHERTON -- While an Atherton family was vacationing in Hawaii, firefighters battled a two-alarm blaze that badly damaged their house near the Bear Gulch Reservoir over the weekend -- a fire that may have been sparked by illegal fireworks.

A woman who was house sitting for the two-story home called in the fire from the house's driveway at 5 Ridgeview Drive around 3:22 a.m., Menlo Park Fire Protection District Battalion Chief Harold Schapelhouman said.

The woman reportedly heard fireworks prior to the fire that caused the upper deck to collapse onto the first floor, Schapelhouman said.

About 44 firefighters with seven engines and two trucks contained the flames just before 5 a.m., he said.

He estimated about $500,000 in damage and said the residents, who are in Hawaii, will not be able to live in the house when they return.

The whole rear of the dwelling and its interior was completely burned, he said.

No injuries were reported.