Experts are cautioning that a full travel bubble halt may not be needed despite half of Australia being in lockdown, provided the Government is confident with state border control measures.

Prime Minister Jacinda Ardern will be joining Covid-19 Response Minister Chris Hipkins and director general of health Ashley Bloomfield to provide an update at 1.30pm regarding the quarantine-free travel arrangements with Australia.

Ardern has cut her recess holiday short, fuelling speculation a full pause of the travel bubble could be on the cards.

However, experts say this might not be necessary provided there was enough confidence in Australia's ability to contain the virus within states experiencing outbreaks.

The announcement comes after an urgent Cabinet meeting on Thursday afternoon with half of the Australian population in lockdown and NSW yesterday recording the most daily cases since the latest Delta outbreak began.

It's understood a complete pause on all travel from Australia was being considered at Cabinet.

A spokesman for the Prime Minister said that an update was expected on Thursday but no update was released.

Now an update has been set for 1.30pm Friday.

The meeting was understood to be a full Cabinet meeting, with ministers meeting despite many being on leave - including Prime Minister Jacinda Ardern and Deputy Prime Minister Grant Robertson.

Half of the Australian population is currently in lockdown and NSW yesterday had the most daily cases since the latest Delta outbreak began.

New Zealand has paused quarantine-free travel with NSW, Victoria and South Australia.

As of Friday morning quarantine-free travel remained open with ACT, Northern Territory, Queensland, Tasmania and Western Australia, subject to conditions including pre-departure tests.

However, a major safety issue remained with up to half of the arrivals from Australia not being checked for negative pre-departure tests.

Otago University epidemiologist Professor Michael Baker told the Herald if the Government was confident in Australia's state border controls, a full pause might not be necessary.

The current "selective" approach saw travel remain open with states such as Tasmania and Western Australia that had done well to keep the virus from crossing state borders, and stamp out quickly any cases they had seen.

Provided the Government was confident in those state border measures, one option would be a more prolonged pause for those eastern states currently experiencing outbreaks, Baker said.

However, the highly-transmissable Delta variant, which is rampant in NSW, meant the threshold for restricting travel was much lower than previously.

There were also questions around the desirability and practicality of keeping the travel bubble open.

If New Zealand did pause the full travel bubble based on the situation in NSW, then it could be for a prolonged period, Baker said.

"I think largely interrupting most travel from Australia would be sensible given how the virus is moving between certain states, particularly in the east.

"But if they do make a decision based on the situation in NSW it could be for a very prolonged period and the question then becomes at what point would it be opened back up."

There was a large number of cases there in the community, multiple points of transmission and with the viral load much higher it could take a long time to stamp it out, Baker said.

Covid-19 data modelling expert Professor Shaun Hendy told RNZ he didn't think a full pause was required, provided there were tight internal restrictions between its states.

"Although the situation in New South Wales is serious and we have seen spread to South Australia and Victoria, at the moment there are quite strong travel restrictions in Australia itself.

"So providing the Government feels confident that it can screen returning travellers who might have been in transit through Victoria for example, or in New South Wales during their time in Australia then I don't think it's necessary to restrict travel from other states at this stage."

This morning an automated voice message on the Air New Zealand general inquiries phone line suggested the transtasman travel bubble was already closed.

The automated voice message said: "The New Zealand Government has announced an extended pause on quarantine-free travel between Australia and New Zealand. We are working closely with the Government for people to return home as soon as possible."

Asked about the message, Air New Zealand general manager of customer Leeanne Langridge said it was recorded and uploaded on 5pm on Wednesday, July 21 in response to large increases in call volumes.

"With Quarantine Free Travel paused from a number of Australian states, we found customers were confused about their ability to travel and the team tried to simplify the message. Unfortunately in this case the simplification has led to an incorrect message that the New Zealand Government had announced an extended pause of quarantine-free travel with Australia," Langridge said.

"This is a rapidly changing environment, and our teams are doing their best to get the most up to date information to customers, we apologise that in this case we may have added to the confusion."