Coronavirus cases in NSW have spiked to 403 as health authorities reveal five of those people contracted the virus on a Sydney Harbour party boat cruise.

That’s a jump of 143 infections on the previous daily case numbers – and the highest single-day tally in nearly two months.

The last time NSW had more than 400 cases in a day was October 14, when it reported 406.

Another COVID fatality was also reported in the state on Wednesday.

NSW Health said preliminary results indicated two of the five COVID-positive party boat cruisers have the new Omicron variant.

All are isolating at home, while urgent genomic sequencing is conducted to confirm the result.

Authorities are trying to contact about 140 people who signed in with a QR code before boarding the boat on Friday. It left Sydney’s King Street Wharf 9 at 7.30pm and returned about 11pm.

Anyone who was on board, and everyone in their households, must immediately get tested and isolate.

The cruise was jointly marketed as ‘Flow Fridays – 90s Themed Boat Party’ and ‘Freaky Sunday Afrovibe: The Last Dance’.

Wednesday’s virus cases were diagnosed from 92,566 tests – up from 58,706 tests the previous day.

The first dose adult vaccination rate in NSW is unchanged at 94.7 per cent, while 92.9 per cent of people 16 and older have had both doses.

More than 81 per cent of teens aged 12 to 15 have had one vaccine dose and 77.3 per cent are fully jabbed.

There are 151 virus patients in NSW hospitals. They include 25 in intensive care.

Thirty-one cases of the Omicron coronavirus variant have so far been confirmed in NSW.

A cluster linked to a climbing gym in Sydney’s south-west and two schools has increased to 20, with more cases expected.

Chief health officer Kerry Chant said on Tuesday the source was believed to be a traveller who had been in Nigeria and arrived in Sydney from Doha on flight QR908 on November 23.

“It’s expected that the numbers linked to this cluster will rise as further results are confirmed over the coming days,” she said.

NSW Health is still trying to determine how contagious the Omnicron variant is and how it is transmitted compared with other variants, such as Delta.

“We are working with our international counterparts to rapidly gain a better understanding about the nature of this new variant,” Dr Chant said.

“We are also working to understand the severity of the new variant and importantly how effective vaccines are at offering protection against severe disease.”

-with AAP