Gunman remains on the run after shooting outside Greenacre school

A gunman remains at large after a man was shot outside a western Sydney primary school this morning.

St John Vianney Primary School was put in lockdown after the drive-by shooting at Pandora Street in Greenacre, about 9.20am.

The victim, believed to be in his mid-30s, was struck in the left knee after three shots were fired from a vehicle.

The school lockdown was lifted just after 10.30am.

"The children and staff are all safe," Mark Rix, head of communications for Sydney Catholic Schools, told AAP.

Off-duty registered nurse Sam Abboud was first on scene, and wrapped the man's wound in a tea towel.

"He just kept saying, 'I got shot, I got shot', he looked a bit pale in the face," Mr Abboud told 9NEWS.

"I just put a bandage around his leg, applied some pressure to the wound."

Earlier, police had cordoned off a 100m stretch of Pandora Street.

Parents were given the option to pick up their children after their shooting.

The victim was taken to Liverpool Hospital for surgery in a stable condition.

He is not cooperating with police.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000.