SF man seriously injured in UN Plaza stabbing

A man was attacked in United Nations Plaza in downtown San Francisco on Thursday. A man was attacked in United Nations Plaza in downtown San Francisco on Thursday. Photo: Michael Macor, The Chronicle Photo: Michael Macor, The Chronicle Image 1 of / 1 Caption Close SF man seriously injured in UN Plaza stabbing 1 / 1 Back to Gallery

A San Francisco man suffered life-threatening injuries after another city resident stabbed him during a fight in United Nations Plaza Thursday afternoon, police said.

The attacker, a San Francisco man in his 50s, was yelling and got into a fight with the victim, a man in his 20's, according to Sgt. Michael Andraychak, a police spokesman.

The older man stabbed the victim multiple times, police said.

Bystanders stepped in during the attack, and responding officers took the suspect into custody. The suspect’s name was not released because he had not been booked into jail, Andraychak said.

The victim was taken to a hospital and was admitted with life threatening injuries, authorities said.

The suspect was also being treated at the hospital for a wound to his hand, believed to be caused by his own knife. Authorities said he was expected to be booked on suspicion of attempted murder.

Jenna Lyons is a San Francisco Chronicle staff writer. Email: jlyons@sfchronicle.com Twitter: @JennaJourno