SAN FRANCISCO -- Investigators searched through the debris Tuesday from a suspicious three-alarm house fire in San Francisco's Potrero Hill neighborhood that damaged three buildings and caused more than $1 million in property and contents damage.

Firefighters responded around 11:15 p.m. Monday after a fire broke out at a three-story home at 1914 20th St. The fire reached a third alarm at 11:23 p.m., according to a dispatcher.

The blaze burned for more than an hour and fully engulfed all floors of the home before firefighters brought it under control at 12:23 a.m., the dispatcher said.

The home where the fire broke out sustained $800,000 in property damage and $25,000 in damage to its contents, San Francisco Fire Department spokeswoman Lt. Mindy Talmadge said.

A nearby home at 1906 20th St. suffered $100,000 in property damage and $25,000 in damage to its contents while another home, at 1924 20th St., sustained around $5,000 in property damage, she said.

A cause of the fire remained under investigation.