A top epidemiologist is surprised at the blanket ban on travel to Australia, as devastated travellers voice heartbreak and frustration at the travel bubble pause.

The quarantine-free travel bubble with Australia has been stopped for three days as of 10.30pm last night, the first time the bubble to all Australian states has been paused.

University of Otago public health expert Professor Michael Baker told Newstalk ZB he was surprised how extreme the ban was.

He said a previous ban on travel from New South Wales was because of an expanding outbreak with the highly contagious Delta variant of Covid-19.

"I'm surprised this suspension has been extended to all of Australia because some states and territories have done at least as well as New Zealand in terms of sustained elimination."

Baker said some states had shown an ability to quickly close borders when neighbouring states had outbreaks.

Travellers with ruined plans spoke of their anguish and disbelief.

"We haven't see our elderly parents since September 2019. We have endured the horrendous Melbourne lockdown," one man told the Herald.

"We have been vaccinated. We have had clear Covid tests. There were no new cases in Melbourne today. We are New Zealanders."

He said his parents were seriously ill and desperate to see him.

"My wife's parents have no other children in New Zealand. This is cruel. Politicians seem to have no idea of the mental anguish caused by this type of blunt instrument approach," he added.

"We are Kiwis, vaccinated, and Covid-free."

"Twelve hours before we fly they do this to us. If they stop us travelling when there are no new cases in our city of 4.5 million, then what hope of lifting ever?"

Another Herald reader said she was already vaccinated and the news came at the worst time.

"As soon as they announced the transtasman bubble me and my mother, originally from Australia, booked flights to come back and see our family.

"We left on Sunday and were hopeful after weeks of no lockdown in Australia. Almost as soon as we arrived in Brisbane, Sydney went into lockdown and all the states closed their borders to Sydney."

She then travelled to Canberra and was planning on flying yesterday, when travel to New Zealand was totally suspended.

"We had planned to travel through Sydney to go back to New Zealand as we could not get a direct flight from Canberra."

She said Air New Zealand was forced to cancel her flights.

"Meanwhile, only two new cases had appeared outside of the managed Sydney cluster, one in the existing Melbourne cluster and one in the north.

"Me and my mother are both fully vaccinated and have not even been in the same states as any cases, yet if we were to travel back to New Zealand we would have to go into MIQ for two weeks and spend however many thousands to pay for it."

She said she was stuck in Australia, with no income, no idea when she will go home and out of pocket for multiple flights already.

"It would have been nice if we could have at least had a few hours even to try get home rather than being stranded with nothing to do but wait."

Yesterday, Sydney recorded 29 new cases, and the Northern Territory and Victoria recorded one community case each.

She said the New Zealand Government had "completely over-reacted" and she suspected other people were in a similar situation.

Baker said decision-makers were probably especially worried about the Delta variant.

A positive Covid-19 case who travelled to Wellington from Sydney earlier this month was confirmed as having the Delta Covid-19 variant.