A fatal stabbing occurred this afternoon outside the U.S. Post Office branch at 18th & Diamond in the Castro.

Tipster Randall D. first alerted us to the incident, and SFPD public information officer Giselle Talkoff confirmed that the call came in at 2:54pm. She said officers found the man, who appears to be in his 60s, on the sidewalk outside the post office, with a knife sticking out of his chest. The man was pronounced dead at the scene.

Talkoff said police remain unsure whether the stabbing was self-inflicted, or inflicted by a suspect. 

Several tipsters wrote in to inform us of the incident. "My boyfriend saw police units in the area and a body being covered," said Hoodline tipster Peter H. "A Mollie Stone's worker said it was a stabbing."

"Sadly but true, I just saw a man stabbed in his chest on the side of the 18th Street Post Office," added Nextdoor user Santos C. "Officers are there right now. Poor man. I think he is dead."

Shortly after the incident at the post office, tipster Tai K. says he saw police officers entering the building that houses Eureka Barber Shop (4222 18th St.), which is just down the street. The barber shop was also the site of police activity in October. Talkoff could not confirm if anyone in the building was being investigated in relationship to the stabbing.

Police are encouraging locals to avoid the area, and Muni lines have been delayed: 

ATTN: #SFPD activity near 18th & Diamond. 33 re-routes: IB - Haight to Divis. to 18th to reg rte; OB - Castro to Haight to regular route.

— SFMTA (@sfmta_muni) December 12, 2016

Thanks to tipsters Randall D., Peter H., and Tai K. If you have a tip, text Hoodline at (415) 200-3233.

Update, 6:20pm: SFPD Mission Station Capt. Daniel Perea told Andrea Aiello of the Castro/Upper Market Community Benefit District that the stabbing is being treated as a suicide.

If you or someone you know is having suicidal thoughts, visit San Francisco Suicide Prevention, call the crisis line at (415) 781-0500 or text MYLIFE to 741741.