NSW is again dealing with more than 20,000 new cases of COVID-19 as the rapid spread of the new Omicron sub-variant causes a spike reminiscent of the summer surge.

The 20,960 cases recorded in the 24-hours until 4pm on Monday is a spike of nearly 6000 cases overnight.

Two women and two men with the virus died on Monday, the same number as the previous 24-hours.

The deaths of two people in their 70s and two in their 90s brought the total number of deaths in NSW since the beginning of the pandemic to 2031.

There are 1177 people in hospital – 14 more than the previous day – and there are 41 patients in intensive care, an increase of seven.

Health authorities said the state is on the cusp of a wave of new cases as the new more transmissible Omicron sub-variant BA.2 takes hold, with cases predicted to peak early next month before subsiding around Easter.

Despite pleas from authorities to get a booster shot, the rate of adults who got the third protective jab remains unchanged at 58.4 per cent.

NSW Health said 79.2 per cent of young people aged 12 to 15 have had two vaccine doses and 48.9 per cent of children aged five to 11 have had one.