A four-alarm fire in the Castro District left seven residents homeless and injured three firefighters this morning, leaving damage significant enough to close an area street all Thursday morning.

The fire was reported at 12:17 a.m. at 27 Hattie Street, a small street between Market and 17th Streets, KRON 4 reports. By 1 a.m., the blaze had been upgraded to four-alarms, according to the San Francsico Fire Department.

By 2:05, the blaze was "under control," according to the SFFD.

According to ABC 7, officials believe that the blaze began "the garage of one home and spread to the homes next to it." In addition, they report, a ruptured gas line at the front door of the structure fed the flames.

Another factor in the swift spread of the fire: Balloon construction, which "means there's no fire stops between the floors so there's a way that the fire could travel from the first floor straight up to the roof," SFFD Battalion Chief Paul Crawford told ABC 7.

"There's no fire stops, wood blocking that would stop the fire from spreading fast," Crawford said.

While current day buildings are designed in a way to prevent this issue, older buildings are not. And the building that burned is clearly an older one, as KRON 4 reporter Will Tran tweets that it was bought in 1887 "for 10 gold coins."

According to the SFFD, three firefighters were injured as they fought the fire. Two were treated at the scene, and the third was transported to the hospital with an injured wrist.

All seven residents — five adults and two children — escaped safely.

A female tabby cat, who was spotted running out the front door as the melee began, is still missing, and area residents are asked to me on the lookout for any stray cats.

As of publication time, Hattie Street remains closed as firefighters clean up the scene.

According to the SFFD, the cause of the fire remains under investigation.

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