SEPTA transit police shot a 48-year-old man who they say attacked three people with a knife — including a woman working as an unarmed security guard — at a SEPTA subway station in Center City on Monday night.

Around 8 p.m., officers responded to the Walnut-Locust Station on the Broad Street Line for a report of a man attacking people with one or two knives, authorities said. A woman working for Extrity, a private firm hired to bolster security in the transit system, , was stabbed in the neck, authorities said.

Guards from the firm, are not armed, said Andrew Busch, a SEPTA spokesperson.

The suspect entered the subway station wielding two knives, one in each hand, said Busch. He poked and slashed two people on the northbound platform before attacking the guard as she tried to intervene, Busch said. The man fled the station after the attacks, which took around two minutes, he said.

Two SEPTA officers found the assailant on the street level, near City Hall, still holding the two knives, according to Busch. One officer deployed his Taser, but it did not deter the suspect, Busch said. The man initially tried to run, he said, then — still holding the knives — moved toward the officers, and one of the officers fired his gun, striking him three times.

The 48-year-old suspect — whose name authorities did not release — is in critical, but stable condition at Thomas Jefferson University Hospital, said Busch.

The security guard was also taken to Jefferson, where she was treated for a stab wound to the neck. The two other victims suffered minor injuries and were treated and released, Busch said.

The incident marked the latest violence to occur on the SEPTA transit system.

On Nov. 19, a 16-year-old girl fired a gun into a crowd of juveniles on the 15th and Market Street station concourse. The girl, whom authorities did not identify because she is a juvenile, is expected to face charges of aggravated assault and firearms violations.

Last month, a 21-year-old Belmont woman who police say shot and killed a SEPTA bus driver in Germantown was charged with murder and related crimes. Zhontay Capers, of the 4300 block of Reno Street, was accused of fatally shooting Bernard N. Gribbin, 48, a Route 23 SEPTA bus driver, police said.

Monday’s incident unfolded as SEPTA and the transit police union continue tense contract negotiations.

SEPTA and the Fraternal Order of Transit Police Lodge 109 are deadlocked in contract negotiations that have been conducted against a backdrop of concern about the safety of transit riders and employees.

Leaders of the 170-member union, which represents patrol officers, decided last week to put their plans for a strike on hold until Dec. 13 at which point the members will decide whether to strike after a formal analysis of the transit agency’s latest contract offer.

The transit officers union says it was promised the same financial terms given to TWU Local 234, the agency’s largest, which represents operators of buses, trolleys and transit trains.

Wages and other supplemental pay for training, uniforms and incidentals are the crux of the dispute.

Lodge 109 says that its ranks are about 25% below the budgeted headcount and that officers continue to leave for better-paying jobs at other law-enforcement agencies in the region, even as SEPTA has recruited police academy cadets and hired some experienced officers.

Staff writer Thomas Fitzgerald contributed to this article