STORY: This stadium in Beijing has been turned into a makeshift fever clinic as authorities in China reported five more deaths.

It is one of hundreds of similar centers that are being added to major cities.

Efforts to expand intensive care units and build these clinics are ramping up across the country, in a desperate bid to prevent the wider spread of contagious disease in hospitals -

Mounting signs the virus is battering China's fragile health system.

China this month began dismantling its stringent "zero-COVID" regime of lockdowns and testing after protests against curbs.

Now, as the virus sweeps through a country of 1.4 billion people who lack natural immunity, having been shielded for so long, there is growing concern about possible deaths, virus mutations, and the impact on the economy and trade.

Xu Wenbo, an official with the Chinese Center for Disease Control and Prevention, told reporters new mutations would occur but played down concerns.

He added that the possibility of new strains becoming more lethal is low.

International concern is also growing over Beijing's surprise decision to let the virus run free.

U.S. State Department spokesperson Ned Price said on Monday (December 19) the potential for the virus to mutate as it spreads in China was "a threat for people everywhere."

“The toll of the virus is of concern to the rest of the world given the size of China's GDP, given the size of China's economy."

Speaking at the same news conference as Xu, the head of Peking University First Hospital's infectious disease department Wang Guiqiang said only deaths caused by pneumonia and respiratory failure after contracting COVID would be classified as COVID deaths.

Heart attacks or cardiovascular disease causing death of infected people will not get that classification.

In total, China has reported just 5,242 COVID deaths since the pandemic emerged in late 2019, a very low toll by global standards.

But there are rising doubts that the statistics are reflecting the true impact of a disease ripping through cities after China dropped curbs on December 7.

Since then, some hospitals have become inundated, pharmacies emptied of medicines.

Many people have gone into self-imposed lockdowns.

In Beijing, delivery workers were seen crowding at pharmacies to pick up medicines.

Some health experts estimate 60% of people in China - equivalent to 10% of the world's population - could be infected over the coming months, and that more than 2 million could die.