An intruder has been shot in the buttocks with an arrow after trying to steal a car in Sydney's south-west, police say.

A 68-year-old man and his wife were in their home on Glanara Court, Wattle Grove, when a unknown man broke in about 5.20pm on Sunday.

The man stole cash and property from the bedroom and took the keys to the couple's Nissan X-Trail, police said

He then went to the garage and started the car.

However, as he tried to reverse out of the garage, the 68-year-old confronted him.