The 18-year-old was taken to Westmead Hospital in a serious condition and is believed to be undergoing surgery.

"A number of shots were fired from a vehicle into a house at Blackwood Road, Merrylands," a police spokesman said.

"There were a number of other people in the premises, family presumably, but I don't know."

The alleged drive-by took place in the minutes after midnight this morning.

A report has said as many as 12 shots were fired into the house, though police were unable to confirm the number.

The duty officer at Merrylands police, Peter Nixon, said there was a family of five in the house at the time.

All have been spoken to by police, although they are unable to establish a motive for the attack.

Inspector Nixon said it did not appear the 18-year-old had been the specific target of the shooting.

"It's early stages at the moment. We will still be doing a lot of forensic ordinary old police detective work," he said.

"It's a bit early for a motive but obviously someone didn't like somebody sometime. It could even be the wrong house."

Neighbours described the victim as a nice boy from a large family this morning.

"They are a good family, a nice family," a neighbour, who did not want to be named, said. "I just say hello, I don't see nothing bad."

Police have interviewed neighbours but could not get a registration number for the car or an indication of how many people were inside.

The best description is of it being light coloured.

Westmead Hospital confirmed the man was treated for both head and eye injuries and remained in a serious condition.

"It's very sketchy, the details around the incident," a hospital manager said.