A group of Muslim supporters has outnumbered protesters calling for Parramatta Mosque to be closed down, a week after a 15-year-old worshipper fatally shot a police employee a few blocks away.

The street outside the mosque in Sydney's west has reopened after the two groups gathered there on Friday afternoon.

There was a large police presence with dozens of officers from general duties, the riot squad and mounted police maintaining an exclusion zone to keep the two groups at opposite ends of the block.

On one side of the exclusion zone, a small group of about 35 people were calling for the mosque to be shut down.

Metres away, a group of approximately 150 people stood with signs supporting the Muslim community.

Farhad Jabar shot dead police accountant Curtis Cheng outside the New South Wales Police headquarters last Friday.

Police said Jabar went to Parramatta Mosque where he changed into a black robe before carrying out the attack.

Jabar was shot dead when officers opened fire.

Members of Curtis Cheng's family lay flowers outside NSW Police headquarters at Parramatta. ( ABC News )

Earlier, members of Mr Cheng's family laid flowers outside the police headquarters.

Meanwhile outside the mosque, members of the anti-Islamic group used a megaphone to ask the pro-Islamic group "why they were colluding with Muslims".

They also urged Parramatta Mosque to reject terrorism and sharia law.

The chairman of Parramatta Mosque Neil El-Kadomi denounced terrorism this week and told worshippers "if you don't like Australia, leave".

Sharia law does not exist in Australia.

Pro-Islamic protester Hady Saleh said he went to the protest to protect the mosque.

"Because during the week, unfortunately, we had groups of people that had very un-Australian actions coming and trying to attack the mosque and the Muslims," he said.

He said it was appalling that Mr Cheng was killed and the majority of Muslims did not endorse violence.

"[It is] something that unfortunately did happen last week at Parramatta at the police station but it does not mean that we all represent this type of action," he said.

"So today we're all standing here in solidarity, Muslims and non-Muslims alike, together to form one voice against these racist, which don't belong in Australia."

Anti-Islamic protesters outside Parramatta Mosque. ( ABC News: Lucy Carter )

Mr Saleh said he hoped the police would put a stop to anti-Islamic "thugs".

Another pro-Islamic protester said Muhammad Ibrahim he was not there to retaliate against the anti-Muslim group.

"We're here to show them what Islam is all about," he said.

"It's all about peace."

He said the mosque would not have anything to do with the shooting last week and he believed Jabar was a victim of extremists.

"I don't blame the kid. I blame whoever brainwashed him," he said.

"I don't think the mosque has anything to do with it at all. I think [there is] more chance the mosque will take him away from that stuff."

Several other members of the mosque had their homes raided and four men were arrested this week by police investigating the shooting.

An 18-year-old remains in custody and is still being questioned by police.

Police had expected 300 or 400 protesters to turn up to this afternoon's rallies.

Earlier, Superintendent Wayne Cox said police would make sure the protests remained peaceful.

"It's one of those situations where you have to be careful and read the situation as it unfolds," he said.

"Obviously we have a range of intelligence coming in to us and we're acting with that intelligence to make sure we have the safety of the community at broad in mind and that's what we're here to do, to protect the community."