Man stabbed in the back in Sydney's west

A man aged in his 20s has been stabbed in the back outside a gym in Sydney's west.

He was attacked in Bankstown before running into a gym on Marion Street to get help around 2pm on Friday, police say.

The man was taken to Liverpool Hospital, where he remains in a stable condition.

A crime scene has been established with people in nearby businesses stuck inside the area.

"Everyone knows each other. It's like a neighbourhood here. It's very frightening," said a worker, who asked not to be named.

Police have asked for any witnesses to come forward.