Chinese health officials acknowledged "shortcomings and difficulties" in their initial response to a fast-spreading new virus as the death toll soared to nearly 500 Tuesday.

The powerful Standing Committee of the Politburo issued a statement saying officials who had failed in their duties would face discipline. It pledged better responses to emergencies in the future.

Chinese President Xi Jinping warned that failing to halt the outbreak could erode social stability in the nation of more than 1.4 billion people.

"The outbreak is a major test of China's system and capacity for governance," Xi said, according to state media. "We must sum up the experience and draw a lesson from it."

More than 20,000 cases of the virus have been confirmed around the world, fewer than 300 of them outside mainland China. Eleven of them are in the U.S.

The death toll was at 492, all in mainland China except for one in Hong Kong and one in the Philippines. More than 2,000 hospital workers in Hong Kong went on strike for a second day Tuesday to demand that the border with mainland China be closed in response to the outbreak.

The total number of cases worldwide stands at 23,892. Based on the latest figures, the coronavirus fatality rate is 2.1%, a figure that has been holding steady throughout the epidemic. Overall, that compares with a fatality rate of 9.6% for SARS.

The virus has had the harshest impact among the elderly and those with other health problems. Jiao Yahui, a National Health Commission official in China, said more than 80% of those who have died were older than 60, and more than 75% had an underlying disease.

Sylvie Birand, director for global infections hazard preparedness at the World Health Organization, said it was "very early" in the outbreak. She declined to describe the outbreak as a pandemic and said it remained mostly contained in China.

"Currently we are not in a pandemic," Birand said. "We are at a phase where we have an epidemic of coronavirus with multiple foci and we try to extinguish each of these foci."

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The U.S. Centers for Disease Control and Prevention said Tuesday that it does not recommend face masks to help prevent the virus, saying it is not spreading in communities in the U.S. Rather, the CDC urged precautions common for combating the flu, such as washing hands often and avoiding contact with people who are sick.

Tedros Adhanom Ghebreyesus, WHO director-general, on Tuesday reiterated his call to all countries not to impose restrictions that" unnecessarily interfere" with international travel and trade.

"Such restrictions can have the effect of increasing fear and stigma, with little public health benefit," Tedros said. "Where such measures have been implemented, we urge that they are short in duration, proportionate to the public health risks, and are reconsidered regularly as the situation evolves."

On Friday, the Trump administration declared the coronavirus outbreak a public health emergency in the United States. U.S. citizens who have been in China's Hubei province and are returning to the U.S. will undergo health screenings and be monitored during mandatory quarantines of up to 14 days, officials said.

The U.S. also announced a suspension of entry into the United States of foreign nationals who pose a risk for the transmission of the virus. And multiple airlines have halted or curtailed China flights.

France, which has six confirmed cases of the virus and has evacuated hundreds of people citizens on two flights, on Tuesday joined Britain in warning against any non-essential travel to China and suggesting that all its citizens in China leave while the coronavirus is still spreading.

Contributing: The Associated Press