Authorities fear NSW residents are taking the COVID-19 threat too lightly, with a key measure of virus infection creeping higher than in Victoria.

NSW recorded 15 new cases on Saturday, five of which are directly or indirectly connected to the cluster originating at the Crossroads Hotel in Casula, southwest Sydney, that now numbers 45 people.

Case numbers in NSW are considerably lower than in Victoria, which tallied 217 new infections and three deaths on Saturday.

But there are concerns about NSW’s reproduction rate, which indicates the number of people infected by a single positive case and is considered crucial to controlling the spread.

Acting Chief Medical Officer Paul Kelly has revealed that while Victoria’s reproduction rate is effectively at one, in NSW it has climbed to 1.4.

“People are more mobile, they are mixing in greater numbers,” he said.

“And there are suggestions from that modelling that people are not taking those messages about physical distancing, hygiene and so forth … as seriously as they currently are in Melbourne.”

Prof Kelly noted that while the figure did not necessarily translate to higher numbers of cases, it demonstrated that the potential for transmission was higher in NSW than in Victoria.

“The message to people in southwest Sydney, please be careful,” he said.

Prof Kelly said there were good indications the lockdown was working in Victoria, where Saturday’s numbers were half the record infections announced a day earlier.

The spread of the coronavirus in Victoria and worrying trends in NSW have prompted Prime Minister Scott Morrison to cancel the planned sitting of federal parliament early next month.

Acting on the advice of Prof Kelly, Mr Morrison has written to the Speaker of the House of Representatives to request that the sitting fortnight commencing August 4 be cancelled.

Parliament was due to sit from August 4 to 13, and will now not meet again until the next planned sitting fortnight starting on August 24.

But Prof Kelly said there will need to be substantially lower rates of community transmission in Victoria, and no worsening of the situation in NSW or other jurisdictions before he was happy with parliament gathering in late August.