[Update: As of 9:30pm tonight, the fire is out. Unfortunately it was the deck of reader Alan Beach-Nelson, but fortunately there appear to be no injuries:

This would be our home. Thankfully just our rear deck is destroyed. An errant ember while we were out all day seems to be the cause. Our pets are all safe thanks to quick acting neighbor Duncan at Vanguard and our neighbor Mary Edna. Huge thanks to our neighbor Laura of growsf for calling it in. Biggest thanks to sffd for taking care of it so quickly. Alan & Daren Beach-Nelson.]

We're getting reports of a fire on Castro Street between 20th and 21st streets.

Massive fire across the street from me at liberty and Castro. Big hand for #sffd for the quick response.

— Erik Brown (@theEABrown) June 21, 2015

According to the SFFD scanner, the fire apparently broke out on the back deck of a residential structure at 720 Castro St. News first broke about the fire around 7pm:

Major house fire off Castro near 21st. Getting worse as we watch. Fire trucks approaching.

— Wilson Hardcastle (@WilloSF) June 21, 2015

We have no details yet about whether the fire has been contained or whether there are any injuries, but we will update accordingly.

Thanks to reader RM for the tip.