A teenager is having surgery after being stabbed during a fight at a Perth bar, while another man has been knocked unconscious in a separate incident outside a Perth bar.

Police said the 18-year-old man was stabbed during an altercation at the Shape Bar in East Perth about 1am on Sunday.

The victim was stabbed when two groups men began fighting inside and outside the bar, police said.

He is having surgery at Royal Perth Hospital.

In a separate incident, a 26-year-old man has been charged after allegedly punching another man outside a Perth bar so hard that he fell to the ground and was knocked unconscious.

Police say on Saturday night, a 24-year-old man was trying to enter a bar on Francis Street when the accused man intervened in the man’s discussion with door staff, argued with the victim and hit him.

He was arrested at the scene and has been charged with assault occasioning bodily harm.

The victim was taken to Royal Perth Hospital for treatment and later released.