Two bullets have hit a school in Sydney's west, in what police believe may have been stray shots from a drive-by shooting.

Officers were called to Lurnea Public School, on West Street, on Wednesday morning after reports of a bullet hole in a window.

Police said there may have been another bullet hole in another window, but it was repaired before officers were called.

Liverpool Local Area Command duty officer, Inspector Jennifer Collins, said the bullet hole was found in a classroom window.

It was believed the shots were fired on Monday night or early Tuesday morning during a drive-by shooting, Inspector Collins said.

"It's not believed that the school was targeted at this stage," she said.

Police said they found a lead fragment from one of the school walls yesterday.

Officers also searched a house in Lurnea and allegedly found a metal replica pistol hidden under a mattress.

Police continued to investigate the shooting and the person who allegedly owned the replica, Inspector Collins said.

Police asked anyone with information to phone Crime Stoppers on 1800 333 000.