A man believed to be in his 20s has been shot dead during a “targeted” home invasion in Sydney’s south-west, police say.

Emergency services were called to the Glen Alpine home about 3:40am.

Campbelltown City Police Area Command Acting Superintendent Gretchen Atkins said the man died at the scene.

“We believe at this point in time it is a targeted attack,” she said.

“That’s all the information we have been able to gather at this point in time, it is really early stages of the investigation.”

A police officer stands in the doorway of a house that has a car parked out the front of it.

Emergency services were called at about 3:40am on Tuesday. (ABC News)

Police said they were told the unknown offenders left the scene shortly before officers arrived.

A crime scene has been established and an investigation is underway with assistance from the State Crime Command’s Homicide Squad.

A report will be prepared for the coroner.