Another 37 people in NSW have tested positive to the coronavirus, including six guests at the same wedding, bringing the total number of infections to 171.

Key points: Among 37 new cases are six people who attended a wedding at Stanwell Tops in the Illawarra region on March 6

Among 37 new cases are six people who attended a wedding at Stanwell Tops in the Illawarra region on March 6 Health authorities are encouraging only those who have returned from overseas and have symptoms to get tested

Health authorities are encouraging only those who have returned from overseas and have symptoms to get tested Police have the power to force people to comply with self-isolation rules, with fines of up to $11,000 for individuals

It is the highest increase in new cases in the state in a single day.

The Health Minister Brad Hazzard said it was likely there would be an exponential increase in coronavirus cases in the next few weeks.

It comes as RSL NSW announced it had cancelled all public Anzac Day commemoration services, saying the risk to the public was "too great".

"Given the significant concerns around the spread of COVID-19, we simply cannot allow such large gatherings as we see each year on Anzac Day to go ahead," acting RSL NSW state president Ray James said.

Racing NSW has also announced this Saturday's $3.5 million Golden Slipper at Rosehill Gardens in Western Sydney will be run behind closed doors.

Mr Hazzard said 67 of NSW's cases were acquired overseas, while 44 cases were transmitted within Australia.

He said it was still unknown how 17 cases contracted the virus.

Mr Hazzard said the infection rate was still low, given more than 25,000 tests had been conducted.

"So I would remind the community of the importance of being with us in partnership in trying to minimise the virus, but also understand that the number of people who are being impacted are still relatively small compared to the total number of tests and the broader population," he said.

He said authorities were trying to contact people on Qantas flight QF-8 that arrived in Sydney from Dallas on March 11, and Virgin Flight VA-2 that arrived in Sydney from Los Angeles, also on March 11.

NSW chief health officer Dr Kerry Chant also said there were six confirmed cases of coronavirus among guests who attended a wedding at Tumbling Waters Retreat at Stanwell Tops on March 6.

The owner of the wedding venue said she had not been contacted by NSW Health.

Sonya Keller said she was unaware until earlier today when the bride contacted her by text to say some of the guests had tested positive.

"[She] said we should have surely been contacted by NSW Health if there was an issue … nothing at all," she said.

"Well as far as I know, all of my staff are well and of course, we are concerned, like everybody.

"It's an unknown thing and now we can take measures now that we know about it."

Dr Chant said it was important that only people with symptoms who had recently returned from overseas be tested for coronavirus.

"If we're swamped with a lot of testing which is of low value, low yield, it actually means that there could be delays for us finding these cases, that are actually putting the community at risk," she said.

Police to enforce self-isolation

Earlier, the NSW Premier Gladys Berejiklian said police would force people to stay at home if they did not voluntarily comply with Australia's new coronavirus self-isolation rules.

Yesterday, the Prime Minister said anyone returning to Australia from overseas would be required to self-isolate for two weeks.

The policy came into effect at midnight, and this morning, Ms Berejiklian confirmed police would target anyone flouting the crackdown.

"We do have that provision. We'll be enacting that," she said.

"We can't pretend that these are normal circumstances, because they're not.

"We can't pretend that it is business as usual, because it's not."

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Ms Berejiklian also encouraged people to let authorities know if they saw others refusing to self-isolate.

"People should report these cases of people turning up to work when they shouldn't," she said.

"If they're engaging in community and social life and they shouldn't, let us know.

This morning special state powers were enacted to force organisers and corporations to obey a ban on public gatherings of 500 people or more.

Mr Hazzard said people who failed to comply with the new laws could face up to six months in prison and a fine of up to $11,000.

Corporations would face larger fines, Mr Hazzard's office said in a statement.

While large gatherings are banned, schools and universities will remain open.

Despite that, a primary school in Sydney's south west was closed this morning, after a visitor tested positive for coronavirus.

St Christopher's Catholic Primary School, in Panania, is closed for cleaning today.