A manhunt is underway in the United States for a suspect who police say killed a man on the street while streaming it live on Facebook.

In the video, suspect Steve Stephens walked up to an elderly man and shot him, authorities said.

The video of the incident was up for about three hours on Facebook on Sunday (US time) before it was removed.

The victim has been identified as 74-year-old Robert Goodwin Sr.

“What happened today was senseless,” Cleveland police chief Calvin Williams said.

Mr Stephens claimed to have killed more than a dozen other people but Mr Williams said police have not verified that information.

A screen grab from the video in which Mr Stephens claims to have killed at least 13 people. Photo: YouTube

“There are no more victims that we know are tied to him,” he added.

Mr Stephens’ Facebook page has been removed.

Mr Williams said authorities have been talking with Mr Stephens’ friends and family.

Mr Stephens should be considered armed and dangerous, police said.

Facebook calls crime ‘horrific’

Cleveland Mayor Frank Jackson publicly urged Mr Stephens to turn himself into police and not to “do anymore harm to anybody”.

“Any problems he is having, we can have a conversation,” Mr Jackson said.

A spokesperson for Facebook described the crime as “horrific”.

“We do not allow this kind of content on Facebook,” they said.

“We work hard to keep a safe environment on Facebook, and are in touch with law enforcement in emergencies when there are direct threats to physical safety.”

This is not the first time an attack has been streamed live on Facebook.

Earlier this year, four people were charged with hate crimes in connection with a video broadcast live on Facebook that showed a mentally disabled man being beaten and taunted, threatened with a knife and forced to drink from a toilet.