A fire broke out on a roof Monday on the commercial corridor of San Francisco's West Portal Avenue, and so far no injuries have been reported but the fire has caused a partial collapse of a building.

The fire started around 11:30 a.m. Monday on the 300 block of West Portal Avenue. the San Francisco Fire Department's Twitter account has posted multiple tweets indicating that this blaze began as a "roof fire" and was affecting six addresses and three buildings including 301 and 309 West Portal Avenue.

By 11:48 a.m. a second alarm had been called, and by 12:30 p.m. it was a three-alarm fire.

Three-Alarm Fire Spreading to Multiple Buildings @CitizenApp

301 W Portal Ave 11:34:01 AM PDT

It was not clear which of the buildings suffered a collapse, or if it was multiple buildings.

The SFFD said the block had been evacuated.

An overhead drone or helicopter photo on KTVU's homepage appears to show that the fire spread around the corner from 301 West Portal to the 14th Avenue side.

The addresses that appeared to be impacted included those belonging to West Portal Cleaners, White Daisy Nail Spa, and Fuji Japanese Restaurant.

This section of the block as it looked in 2014. Photo: Google Streetview