China is experiencing a huge COVID-19 surge after years of hardline containment restrictions were dismantled last month.

A growing number of countries are worried about a lack of data and transparency surrounding China's outbreak.

However the European Centre for Disease Protection and Control argues that the surge of cases is "not expected to impact" the COVID situation in the EU.

Here is why China's COVID wave is sparking concern and what the experts say:

Unreliable data

Beijing has admitted the scale of the outbreak has become "impossible" to track following the end of mandatory mass testing last month.

The National Health Commission has stopped publishing daily nationwide infection and death statistics.

That responsibility has been transferred to the Chinese Center for Disease Control and Prevention (CDC), which will only publish figures once a month after China downgrades its management protocols for the disease on January 8.

China has only reported 15 Covid deaths since it began unwinding restrictions on December 7, shortly after which it narrowed the criteria by which deaths from the coronavirus are recorded.

Passengers of a flight from China wait in a line for checking their COVID-19 vaccination documents as a preventive measure against the COVID-19 coronavirus, after arriving at the Paris-Charles-de-Gaulle airport outside Paris, on January 1. Photo: AFP

This has stoked concerns that the wave of infections is not being accurately reflected in official statistics.

Authorities admitted last week that the scale of data collected is "much smaller" than when mandatory mass PCR testing was in place.

CDC official Yin Wenwu said authorities are now compiling data from hospitals and local government surveys as well as emergency call volumes and fever medicine sales, which will "make up for deficiencies in our reporting".

Chinese hospitals and crematoriums are struggling with an influx of patients and bodies, with rural areas hit particularly hard. 

Several countries including the United States, Australia and Canada last week said they were imposing testing restrictions on arrivals from China because of a lack of transparency on infection data.

Piecemeal estimates

Last month, a few local and regional authorities began sharing estimated daily infection totals as the scale of the outbreak remained unclear.

Disease control authorities in the wealthy coastal province of Zhejiang said Tuesday that the number of new cases jumped one million in the past few days, and "the epidemic is expected to enter a peak plateau in January". 

The Zhejiang cities of Quzhou and Zhoushan said at least 30 percent of the population had contracted the virus.

A staff member prepares antigen test kits at a pharmacy amid the COVID-19 pandemic in Hangzhou, in China's eastern Zhejiang province on December 19. Photo: AFP

The eastern coastal city of Qingdao also estimated around 500,000 new daily cases and the southern manufacturing centre of Dongguan forecast up to 300,000.

Officials in the island province of Hainan estimated Friday that the infection rate there had surpassed 50 percent.

But top health official Wu Zunyou said Thursday that the peak had passed in the cities of Beijing, Chengdu and Tianjin, with Guangzhou city officials saying the same on Sunday.

A senior doctor at a Shanghai hospital estimated Tuesday that up to 70 percent of the city's 25 million population may have been infected in the current wave. 

Leaked notes from a meeting of health officials last month revealed they believed 250 million people had been infected across China in the first 20 days of December.

Independent infection models paint a grim picture. University of Hong Kong researchers have estimated nearly one million Chinese may die this winter as a result of opening up.

And health risk analysis firm Airfinity forecast 11,000 deaths and 1.8 million infections per day, with a total of 1.7 million fatalities by the end of April.

New variants?

Many countries have cited concerns over potential new variants as a reason to screen Chinese arrivals for Covid.

But there is as yet no evidence of new strains emerging from the current wave. Top CDC official Xu Wenbo said last month that China was developing a national genetic database of Covid samples derived from hospital surveillance that would help track mutations.

Chinese health experts have said in recent days that the Omicron subvariants BA.5.2 and BF.7 are most prevalent in Beijing, in response to public fears that the Delta variant may still be circulating.

They said Omicron also remained the most dominant strain in Shanghai.

In many Western nations, these strains have been overtaken by the more transmissible subvariants XBB and BQ, which are not yet dominant in China.

Beijing has submitted 384 Omicron samples in the past month to the global online database GISAID, according to its website. 

But the country's total number of submissions to the database, at 1,308, is dwarfed by those of other nations, including the United States, Britain, Cambodia and Senegal.

Recent samples from China "all closely resemble known globally circulating variants seen... between July and December", GISAID said Friday.

University of Hong Kong virologist Jin Dong-yan said on an independent podcast last month that people need not fear the risk of a deadlier new variant in China.

"Many places all over the world have experienced (large-scale infection) but a more deadly or pathogenic variant did not emerge afterwards," said Jin.

"I'm not saying that the emergence of a (more deadly) strain is completely impossible, but the possibility is very small."

The EU response

France, Italy and Spain are among around a dozen countries in the world to require COVID-19 testing of passengers arriving from China. 

The EU is to discuss a joint COVID-19 response on Wednesday. 

Malta has no immediate plans to test travellers whose trips originated from China, with health authorities saying they are in direct communication with the European Centre for Disease Prevention and Control (ECDC).

On Tuesday, the ECDC said the variants of the virus circulating in China are already circulating in the EU "and as such are not challenging for the immune response of EU/EEA citizens". 

It also pointed to the high level of immunisation and vaccination levels in the EU.

The health agency previously said that systematic screening of travellers was unjustified and its latest statement reiterated its position that a "surge in cases in China is not expected to impact the COVID-19 epidemiological situation in the EU/EEA".