State media in China have played down the severity of its surge of COVID-19 infections ahead of an expected briefing by its scientists to the World Health Organisation, which is hoping for detailed data on the evolution of the virus.

China's abrupt U-turn on COVID controls on December 7, as well as the accuracy of its case and mortality data, have come under increasing scrutiny at home and abroad and prompted some countries to impose travel curbs.

The policy shift followed protests over the "zero COVID" approach championed by Xi Jinping, marking the strongest show of public defiance in his decade-old presidency and coinciding with the slowest growth in China in nearly half a century.

As the virus spreads unchecked, funeral parlours have reported a spike in demand for their services and international health experts predict at least one million deaths in the world's most populous country this year.

China reported three new COVID deaths for Monday, taking its official death toll since the pandemic began to 5253.

On Tuesday the Communist Party's official newspaper, the People's Daily, cited Chinese experts as saying the illness caused by the virus was relatively mild for most people.

"Severe and critical illnesses account for 3 per cent to 4 per cent of infected patients currently admitted to designated hospitals in Beijing," Tong Zhaohui, vice president of the Beijing Chaoyang Hospital, told the newspaper.

Kang Yan, head of West China Tianfu Hospital of Sichuan University, said that in the past three weeks, a total of 46 patients had been admitted to intensive care units, or about 1 per cent of symptomatic infections.

The emergencies area at the Zhongshan Hospital in Shanghai was packed with patients on Tuesday, most of them elderly, a Reuters witness said.

Some were in beds in the corridor, covered with blankets and receiving IV treatment while dozens were queuing around them, waiting to be seen by a doctor. It was unclear how many were there with COVID.

The World Health Organisation has urged Chinese health officials to regularly share specific and real-time information on the COVID situation.

The WHO has invited Chinese scientists to present detailed data on viral sequencing at a Tuesday meeting of a technical advisory group. It has also asked China to share data on hospitalisations, deaths and vaccinations.

"I don't think China will be very sincere in disclosing information," said Alfred Wu, associate professor at the Lee Kuan Yew School of Public Policy at National University of Singapore.

"They would rather just keep it to themselves or they would say nothing happened, nothing is new. My own sense is that we could assume that there is nothing new ... but the problem is China's transparency issue is always there."

The United States, France, and others will require COVID tests on travellers from China, while Belgium said it would test wastewater from planes for new COVID variants.

European Union health officials will meet on Wednesday on a coordinated response.

China has rejected criticism of its COVID data and said any new mutations may be more infectious but less harmful.

China's foreign ministry said on Tuesday the entry restrictions imposed by some countries on travellers from China "lacked scientific basis" and were "simply unreasonable".

China will stop requiring inbound travellers to go into quarantine from January 8. But it will still demand a negative PCR test result within 48 hours before departure.

As Chinese workers and shoppers fall ill, concerns mount about near-term growth prospects in the world's second-largest economy, causing volatility in global financial markets.