Armed man holds up Sydney betting agency

A woman working at a betting agency in Sydney's southwest has been threatened by a man with a gun.

A woman working at a betting agency in Sydney's southwest has been threatened by a man with a gun. (AAP)

A man armed with a gun has threatened a woman working at a betting agency in Sydney's southwest before fleeing with cash.

Police said that at 6.30pm (AEDT) on Tuesday the man entered the agency on Villawood Road at Villawood, and threatened the 50-year-old staff member with a firearm.

He demanded money then ran from the scene.

Police are seeking a man described as being of Caucasian appearance, about 185cm tall, of thin build and wearing a long-sleeved shirt.