China says nearly 60,000 people with COVID-19 have died in hospital since it abandoned its zero-COVID policy last month, a huge increase from previously reported figures that follows global criticism of the country's coronavirus data.

In early December, Beijing abruptly dismantled its strict three-year anti-virus regime of frequent testing, travel curbs and mass lockdowns after widespread protests in late November, and cases have surged since then across the nation of 1.4 billion.

A health official said on Saturday that COVID fever and emergency hospitalisations had peaked and the number of hospitalised patients was continuing to decline.

Between December 8 and January 12, the number of COVID-related deaths in Chinese hospitals totalled 59,938, Jiao Yahui, head of the Bureau of Medical Administration under the National Health Commission (NHC), told a media briefing.

Of those fatalities, 5503 were caused by respiratory failure due to COVID and the remainder resulted from a combination of COVID and other diseases, she said.

The World Health Organization, which earlier this week said that China was heavily under-reporting deaths from the virus and called for more information, on Saturday welcomed Beijing's announcement, while renewing its plea for more detailed data.

The UN agency said its Director General Tedros Adhanom Ghebreyesus had spoken with Ma Xiaowei, director of China's National Health Commission, about the latest outbreak, which the WHO said was similar to what had been seen in other countries.

"The reported data indicate a decline in case numbers, hospitalisations, and those requiring critical care," it said, commenting on Beijing's numbers.

While international health experts have predicted at least one million COVID-related deaths this year, China had previously reported just over 5000 deaths since the pandemic began, one of the lowest death rates in the world.

Authorities had been reporting five or fewer deaths a day over the past month - figures inconsistent with long queues seen at funeral homes and body bags seen leaving crowded hospitals.

China, which last reported daily COVID death figures on Monday, has repeatedly defended the veracity of its data on the disease.

On Saturday, Jiao said China divides COVID-related deaths between those from respiratory failure due to coronavirus infection and those from underlying disease combined with the infection.

"The standard is basically in line with those adopted by the World Health Organization and other major countries," she said.

Last month, a Chinese health expert at a government news conference said only deaths caused by pneumonia and respiratory failure after contracting COVID would be classified as COVID deaths. Heart attacks or cardiovascular disease causing the death of infected people would not get that classification.

Yanzhong Huang, senior fellow for global health at the Council on Foreign Relations in New York, said the tenfold increase in deaths announced on Saturday suggested China's COVID policy reversal "is indeed associated with" a sharp rise in severe cases and deaths, especially among older people.

However, he said, it was unclear whether the new data accurately reflected actual fatalities because doctors were discouraged from reporting COVID-related deaths and the numbers included only deaths in hospitals.

"In the countryside, for example, many elderly people died at home but were not tested for COVID due to the lack of access to test kits or their unwillingness to get tested," he said.

Despite worries about infections, air passenger volumes in China have recovered to 63 per cent of 2019 levels since the annual travel season began on January 7, the industry regulator said on Friday.