Man suffers life-threatening injuries in hammer attack in SF

File photo of police squad car at night. Patrol car with lights flashing File photo of police squad car at night. Patrol car with lights flashing Photo: Ron Chapple, Getty Image Photo: Ron Chapple, Getty Image Image 1 of / 1 Caption Close Man suffers life-threatening injuries in hammer attack in SF 1 / 1 Back to Gallery

A 55-year-old man suffered life-threatening injuries early Friday when he was beaten with a hammer in the South of Market neighborhood of San Francisco by a bystander who tried to break up an argument between the victim and the victim’s relative, officials said.

The assault occurred at Division and Brannan streets about 12:40 a.m. after the victim and a family member got into a heated argument on the street, police said.

A 49-year-old bystander attempted to intervene in the argument, causing the victim to become angry, police said.

Officials said that when he was confronted, the bystander picked up a hammer lying nearby and beat the man, whose name was not released.

No arrests were made.

The victim was transported to a hospital.

Sarah Ravani is a San Francisco Chronicle staff writer. Email: sravani@sfchronicle.com Twitter: @SarRavani