Mounting COVID-19 cases in the United Kingdom could see New Zealand slap a flight ban on the coronavirus-stricken Brits.

New Zealand's leaders have expressed dismay towards the UK's handling of COVID-19, and could put the country on a no-fly list should cases explode in line with government predictions.

The stark difference in strategies in London and Wellington was evident this week.

As the UK announced plans to roll back restrictions, New Zealand slapped new obligations on travellers from the only country that can visit: Australia.

Australians looking to utilise the trans-Tasman bubble will now have to produce a negative COVID-19 test within 72 hours of travelling to New Zealand.

Meanwhile, the UK is allowing vaccinated travellers from much of the world to visit without isolation, with far fewer societal rules from July 19.

Those strategies have shown up in case numbers.

New Zealand hasn't seen community transmission of COVID-19 since February, but the UK suffered more than 28,000 cases on Tuesday, with leaders warning that number will continue to grow as it opens further.

Moves in the UK have caused consternation in Wellington.

"That's not something that we have been willing to accept in New Zealand," COVID-19 Minister Chris Hipkins said.

Climate Change Minister James Shaw said the UK was enduring a "human tragedy".

"If you look at the policy response that we've had here, it's both been better for the economy and human health," he said.

"I was flabbergasted at the idea that a government would make those choices."

Mr Shaw said the government should consider counselling UK counterparts against the move, saying "I certainly don't think that there's any harm in having those conversations".

Prime Minister Jacinda Ardern was more cautious.

In comments directed towards COVID-stricken Fiji - but could have easily been directed towards the UK - Ms Ardern said "countries will make their own decisions".

"New Zealand has chosen its path. We did so without necessarily being told by anyone else what we should or shouldn't do but we will always offer advice and what we've learned with anyone who would wish to ask," she said.

"Lockdown for us has saved lives and it's also benefited our economy, but these choices are for governments."

The mounting UK and Fiji cases will have repercussions for New Zealand, given many Kiwis live in both places.

New Zealand severely limits travel from high-traffic countries deemed "very high risk" when more than five per cent of arrivals test positive for COVID-19.

Currently four countries meet that designation: India, Pakistan, Brazil and Papua New Guinea.

Director-General of Health Ashley Bloomfield said officials would be "watching very closely" to see if new countries fit that bill.

"If they do get an increase in cases, we will be keeping a close eye on what that means for the risk of people travelling from the UK, and that will inform our decisions here," he said.