The fire was reported at a two-story home at 376 Harvard St. at 1:55 a.m. San Francisco Fire Department Lt. Jonathan Baxter said Engine 43 arrived to find a fully engulfed second story of the home.
Baxter said a 17-year-old boy who suffered moderate injuries escaped the blaze and told fire crews who arrived at the scene his parents were inside. The boy gave fire crews specific directions of where to find them in the house, according to Baxter.
RELATED: Prepare NorCal: Disaster Preparedness Resources
Fire crews then entered the home and extricated a man and woman. Baxter said the man who was extracted suffered critical injuries and the woman who was taken out of the home by firefighters suffered moderate injuries. All three were transported to a hospital, where the man remains in critical condition, Baxter said.
Three other adults were displaced in the fire, but Baxter couldn't confirm whether they were home at the time of the blaze, which was extinguished at 2:12 a.m.
The cause of the fire is currently under investigation.