A British backpacker is recovering from stab wounds after fighting off a housemate with a knife when he allegedly tried to rape her.

The 23-year-old woman resisted an initial attack before the man returned with a knife and stabbed her several times in the upper body in Sydney, police said.

She managed to get out of the room and found a knife, which she allegedly used to stab her attacker in the chest before escaping.

New South Wales State Police Detective Inspector Despa Fitzgerald said the woman was lucky to be alive.

She said: "She did a tremendous act at the time. Obviously her survival instincts kicked in and she was able to remove herself from the situation.

"Luck is the key word and it's just lucky it didn't hit a major artery in those alleged attacks and for him as well."

Jerry Betrou, who was working in a nearby shop in the inner-city suburb of Redfern, said: "Heard loud screams, psychotic screams, walked out, seen a girl pushed up against the window, blood coming out of her right hand side, 'Help me, help me', and the coppers (police) came and that was it."

The woman was taken to hospital where she had surgery on a punctured lung, local media reported.

One of her friends called police, who reportedly arrested a 27-year-old Mexican man after a short chase on foot.

The man remains under police guard at another hospital after suffering serious chest injuries, according to local media.

A police spokeswoman said the woman and her alleged attacker were "possibly acquaintances" but did not know each other well.

It is thought there were up to 20 people in the house at the time.

A Foreign Office spokesman said: "We are offering assistance to a British national who remains in hospital in Sydney, and will stay in contact with local authorities."