Sydney man shot dead after answering door

A man was shot dead in his home in Sydney's west after answering a knock at the front door, police say.

The 23-year-old was gunned down at his home on Horsley Drive, Horsley Park, late on Thursday night.

Police have blocked off part of Horsley Drive and are searching for the shooter in nearby suburbs.

Superintendent Peter Lennon said it was understood a knock at the door may have preceded the shooting.

"Our inquiries at this stage indicate that he thought he was answering a knock at the door," Supt Lennon told reporters.

Supt Lennon said the man was found dead near the front door when officers arrived at the house about 11.45pm.

He said the man was shot more than once.

Supt Lennon said the man lived with a housemate who was home at the time of the shooting.

The home is connected to a function centre on Horsley Drive.

Supt Lennon said the dead man had not been formally identified but that "if it is the gentleman we think it is, he is not known to police".

"We're not looking at anything in the way of bikie related ... we've got to start from scratch and develop the motive ourselves," he added.

Supt Lennon said officers didn't have the chance to speak to the man before he died.

He said while there was an outlaw motorcycle gang clubhouse nearby, there was no connection between it and the shooting at this stage.

He said the Horsley Drive remained closed between the M7 and Ferrers Rd as police investigated.

The Transport Management Centre is urging motorists to avoid the area through the morning peak.