New South Wales Premier Gladys Berejiklian has labelled New Zealand's decision to pause the travel bubble with Sydney an "overreaction".

Covid-19 Response Minister Chris Hipkins announced yesterday that New Zealand had put a pause on all flights out of NSW as the state reported two community cases of coronavirus, just weeks after both nations opened quarantine-free travel across the ditch.

"That, to me, is an overreaction," Berejiklian said in an interview this morning. "If that's what the department says they must do, that's what she [Prime Minister Jacinda Ardern] does. But I certainly think the response should also be proportionate to the risk."

Berejiklian said NSW health officials were working hard to "stop a super spreading event" with a slate of new restrictions in Greater Sydney over the next three days to minimise the chances of further cases spreading.

Director general of health Dr Ashley Bloomfield said the decision to pause the travel bubble with Sydney was necessary.

"I don't think we're being trigger-happy at all," he told Newstalk ZB's Mike Hosking this morning.

"We think, on balance, it was the right thing to do."

The pause for the next 48 hours was put in place so authorities can watch to see what further results come out of Sydney, he said.

Covid-19 Response Minister Chris Hipkins has paused quarantine-free travel between New Zealand and New South Wales while the source of infection of the two cases announced in Sydney in the last two days is investigated.

Hipkins said yesterday that with several outstanding unknowns in the situation in Sydney, pausing quarantine-free travel with Sydney was the safest option.

"Everything is based on the information you have at the time. There will always be cases that are right at the margin where you need you to gather more information... we are erring on the side of caution."

Hipkins also said the pause could be extended if further information came to light and officials needed more time.

"We indicated when we opened up the transtasman travel bubble [that we] will continue to be cautious, we are continuing to be cautious," he said.

A list of locations of interest has been released by New South Wales health and is published on its website.

Those in Australia who were at a location of interest at the specified times were asked to follow the health advice regarding isolation and testing, and should not travel to New Zealand.