Police say they believe a shoot-out in Sydney's south-west this morning was pre-planned.

Up to 12 shots were traded between two groups firing at each other in cars on Mimosa Road at Greenfield Park.

One of the bullets hit a nearby house with three adults inside just after 2:00am (AEDT), but no-one was injured.

Police say they believe there were a number of occupants in the cars. One group was in a blue Toyota and another in a white sedan.

Sergeant Dave Rose says officers believe they have found one of the cars involved in the shooting.

"Around 3:10am police located a blue Toyota abandoned in Crosio Place at Bonnyrigg," he said.

"That vehicle, which is believed to have been involved in the incident, has been seized for forensic analysis."

Superintendent Peter Lennon says gun crime is increasing.

"Our first thoughts are, it's early days, but two motor vehicles don't come together at 2:00 in the morning and shots start getting fired," he said.

"Something's occurred to bring them together."

He said police in the area are sick of criminals putting innocent lives at risk.

"These are criminals who have got a total disregard for the rest of the state," he said.

"It's only a matter of time before an innocent person is killed."

Strikeforce Moore has been established to investigate the shoot-out.

Police say they do not believe this incident is linked to two drive-by shootings at houses in Auburn and Arncliffe two nights ago.

They are appealing for witnesses with information to come forward.

Superintendent Peter Lennon says someone out there knows what is happening.

"If someone gets killed, you are going to be just as liable as the person that pulled the trigger, if you know what's going to occur or what has occurred," he said.

"You're going to have that stain on your conscience for the rest of your life."