SFPD is asking the public to avoid the 900 block of Market Street, and one tipster has written in saying his office building is currently on lock down.

“Apparently they closed our office front lobby area due to a shooting on 5th and Market," wrote Devon. "I work in the 901 Market building.”

Avoid the area of 900 Market Street due to Police activity and street closures. It is an ongoing investigation. Expect delays. #SFPD #SF pic.twitter.com/g1yUSNxNgq

— San Francisco Police (@SFPD) May 3, 2017

Shots fired in Subway at 900 block Market St pic.twitter.com/1Jfs48Ovwh

— _ (@R27D) May 3, 2017

@BizDevBen @zachtratar @LukeBornheimer @SFPD @SF_emergency @Emergency_In_SF I saw two officers heading toward a crowded Subway - crowd then scattered, and I heard a single gunshot and got down (~11:25am, I was on 5R)

— Michael Shane (@____CLEARLY____) May 3, 2017

ABC7 has reported that the incident may be an officer-involved shooting, but that information hasn't been confirmed. We'll keep you posted.

Update, 12:15pm: A witness told the Chronicle that he saw an officer shoot a man in the chest on Market near Mason, although it is still unclear what exactly happened.

Update, 1:35pm: SFPD Chief William Scott told our reporter on the ground that at 11:22am, two uniform officers on foot beat witnessed a white male stabbing an Asian male near the corner of Market and Turk Streets. One of the officers opened fire.

The stabbing suspect died at the scene; no word yet on the victim's condition.

This is the first officer-involved fatality since Chief Scott took command. Scott stressed that the 1pm press briefing was only a preliminary statement that an investigation would be ongoing, including interviews with the involved officers.

Powell Street Station has reportedly not been affected by the incident, but several transit lines running along Market Street have been temporarily rerouted.

Update, 5/4, 10:33am: According to Bay City News, the medical examiner's office has identified the man fatally shot by SFPD as 26-year-old Nicholas Flusche.