The chairman of a Sydney mosque has told worshippers that "if you don't like Australia, leave" during his first sermon since a teenage extremist who attended the mosque shot dead a man outside NSW Police headquarters.

The comments were reported in Sydney newspapers earlier this morning and Parramatta Mosque chairman Neil El-Kadomi has told those attending Friday prayers that he stands by those comments.

Last Friday's shooting of police accountant Curtis Cheng outside NSW Police headquarters in Parramatta has prompted several agencies to investigate how the 15-year-old killer became radicalised by Islamic extremists.

A week on from the tragedy, Mr El-Kadomi addressed worshippers who gathered for Friday prayers.

Outside, he questioned why police shot dead the 15-year-old gunman, saying it was unfortunate the boy died because now there is no way of knowing his secrets, particularly who gave him the gun.

He also said extremists unwilling to live by Australian standards of peace and tolerance should leave the country.

"You should not abuse the privilege of being Australian, which is very important," he said.

Mr El-Kadomi added that those who do abuse the privilege should "get out".

"We do not need scumbags in the community," he said.

"We have to lift our heads up as Australians.

Men bow their heads in prayer at the Parramatta Mosque. ( ABC News: Luke Rosen )

"We live in this community, in this society.

"We have to accept the good and bad and the ups and downs in this society."

Mr El-Kadomi also urged Muslims in Australia to appreciate how lucky they were to be able to practice their religion openly.

"We live in Australia - people are coming to Australia on boats, they die on the way," he said.

"You didn't have to do that, you are here ... Australia gives us a lot of benefits – you're here and can practice your religion freely."

He told today's congregation a tiny proportion of the community are giving Muslims a bad name, and that parents need to take more interest in their children's lives to prevent radicalisation.

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He said that anyone seen acting suspiciously at the mosque would be reported to police.

Jeremy Jones from the Australia/Israel & Jewish Affairs Council placed flowers at a police memorial before visiting the mosque to lend his support to Mr El-Kadomi's message of tolerance.

The Parramatta Mosque was searched after Farhad Jabar's attack on police headquarters at Parramatta on Friday.

Police also said some of the people later arrested in relation to the attack were known to attend the mosque.

Federal Opposition Leader Bill Shorten endorsed the comments of the Parramatta Mosque chairman.

"Australians, it doesn't matter what religion - if you really hate Australia, well then you should go," he said.

"But I don't think though that that advice is confined to people of one particular religious faith."

Worshippers gather at Parramatta Mosque as chairman Neil El-Kadomi delivers a sermon at Friday prayers. ( ABC News: Luke Rosen )

NSW Opposition calls for inquiry into radicalisation

The State Opposition has called for an urgent inquiry into radicalisation in the state's schools.

Labor's education spokeswoman, Linda Burney, said there had been warning signs about the potential for teenagers to be radicalised by fellow students long before last Friday's shooting.

"There have been warning signs for some months now, almost the whole year, about issues that are bubbling up in schools," Ms Burney said.

"The Government has been slow to respond. There does not appear to be a coherent response."

The Government is currently considering the results of a statewide audit of school prayer groups, which was launched in July after reports a student at Epping Boys High had been preaching a radical form of Islam.

Ms Burney said a bipartisan inquiry should look at better regulating prayer groups, and examine ways to prevent teenagers becoming disenfranchised.

But the NSW Government has told the ABC it has been working on further plans to "enhance current measures".

"The Department of Education has been working in consultation with police on the issue of radicalisation," a spokesperson said.

"These will be announced in due course."

