The Chinese government has suggested that travel restrictions imposed on Chinese arrivals are politically motivated - with New Zealand yet to decide whether it will require mandatory Covid-19 testing for travellers from China.
The United States, United Kingdom, Australia and India are among the nations that have already introduced mandatory testing for arrivals from China.
China has recently seen a surge in Covid cases following the easing of its strict controls and there are fears that cases and deaths are being vastly underreported.
China's last daily Covid-19 update, on 24 December, reported fewer than 5000 cases - but some analysts claim the daily caseload is already over 2 million, and could peak at almost 4 million this month.
A lack of data - and China's announcement that it was easing curbs on travel from 8 January - led to more than a dozen countries announcing Covid-19 testing on arrivals from China.
China's foreign ministry labelled the curbs on travellers from China as "simply unreasonable", saying they "lacked scientific basis".
"We are willing to improve communication with the world," foreign ministry spokeswoman Mao Ning told reporters in Beijing.
"But ... we are firmly opposed to attempts to manipulate the epidemic prevention and control measures for political purposes."
Epidemiologist Michael Baker told Morning Report that New Zealand should require pre-departure Covid-19 testing for travellers leaving from China.
Baker said the government should introduce temporary pre-departure testing for any country with infection waves or new variants.
"The reason is it would reduce the number of infected people getting on flights to New Zealand and that has two big benefits: one, it reduces the number of infected people arriving in New Zealand and secondly, it also reduces the number of people getting infected during flights, which we know happens if you have infected people on flights."
New Zealand has a current Covid-19 rate of infection of 1-2 percent where as China's rate of infection is 10-20 percent, and possibly even greater than that, Baker said.
But it should only be a temporary measure while there were very high rates in China, he said.
Pre-departure testing needed to be based on very clear thresholds to include any country which was having a Covid-19 surge or had a particularly dangerous new subvariant, Baker said.
The World Health Organisation could play a key role and establish international guidelines, he said.
The WHO has expressed frustration that China was not reporting its case numbers and its director-general had said he could understand why countries were looking at these measures, Baker said.
It was not unusual to have pre-event testing which was already used on cruise ships and was a requirement at some conferences, he said.
"It's just another way of reducing the risk of infection for people in those situations."
China required travellers entering the country to have a negative PCR test, so the approach was even-handed, Baker said.
New Zealand needed to manage its borders on the best available evidence and to prepare for more dangerous new variants, he said.
New Zealand was also coming out of the third Omicron wave and infections should drop back to lower levels over the next few weeks, Baker said.
"But as we know of this virus, it looks like the pattern continuing to the future is of continuing evolution of new subvariants, maybe even new variants, that are good at evading our immunity and causing future waves - so that appears to be a pattern we could plan for for the foreseeable future."
China turns down EU's Covid-19 vaccine offer
China has rejected an offer from the European Union to supply an unspecified number of Covid-19 vaccines to help deal with the surge in cases, saying it has an "adequate supply".
Official data shows China has given more than 3.4 billion doses - the vast majority of which are CoronaVac.
The government has so far insisted in using only Chinese-made vaccines, which have been proven to be less effective than other Western-developed mRNA vaccines against the Omicron variant.
- RNZ / BBC / Reuters