Cleaning staff at Lurnea Public School discovered broken glass in a classroom on Tuesday night.

Police informed the school on Thursday that a bullet had smashed through the window and another had gone through the window frame of the school office.

Detectives suspected the shots might have come from a nearby home.

They seized a replica handgun from under a mattress at the home and were continuing to investigate.

``It's just one of these random senseless acts at night,'' Liverpool crime manager Detective Inspector Danny Doherty said.

The school's principal, David Sim, declined to comment but issued a letter reassuring parents.

``Police have advised me that there is no known threat to our school,'' Mr Sim said in his letter.

New South Wales Opposition Leader John Robertson chaired a crisis meeting yesterday of more than two dozen church leaders, business owners and community representatives at a community centre in the western suburb of Greystanes.

He said Premier Barry O'Farrell had done nothing to curb the 60 shootings that had occurred in Sydney's west since the Coalition won government in March 2011.

``Sixty is 60 too many and when there's an innocent victim killed this premier will have blood on his hands,'' Mr Robertson said.

Eighteen shootings have happened in 2012.

Mr O'Farrell accused the state opposition of politicising the shootings, and defended the police response to the attacks.