Investigators were at a 3,500-square-foot home in Atherton Saturday afternoon trying to determine was caused a fire there, Menlo Park fire Chief Harold Schapelhouman said.

The fire was reported to the Menlo Park Fire District at 10:24 a.m. at 51 Hawthorne Drive. Firefighters arrived at the home at 10:28 a.m., and at 10:36 a.m. a second alarm was called, he said.

There was damage to 60 percent of the home and smoke damage to 100 percent of the single-story building. There was at least $750,000 in damage to the structure and between $100,000 and $200,000 to the contents, he estimated.

The fire was controlled at 11:05 a.m.

A couple and their daughter lived at the gated, ranch-style home, which was also a licensed daycare facility, Schapelhouman said.

There were no injuries.

Forty people helped battle the blaze. The Redwood City Fire Department, San Mateo County Fire Department and the Woodside Fire Protection District assisted the Menlo Park Fire District.