This image has been used for illustrative purpose.

The US said Friday it was declaring a public health emergency and temporarily banning the entry of foreign nationals who had travelled to China over the past two weeks to contain the spread of a deadly new virus.

Sweeping new restrictions will also be imposed on American citizens, with those returning from the province at the disease's epicenter placed in facilities for mandatory 14-day quarantines, said Health Secretary Alex Azar.

US citizens coming from other parts of China will undergo health screening at ports of entry and then be placed under monitored self-quarantine at home.

"I have today declared that the coronavirus presents a public health emergency in the United States," said Azar during a briefing at the White House, adding the directives would take effect on February 2 from 5:00 pm eastern time (2200 GMT).

"Foreign nationals, other than immediate family of US citizens and permanent residents, who have traveled in China within the last 14 days will be denied entry into the United States for this time," he added.

US citizens coming from other parts of China will undergo health screening at ports of entry.

The restrictions apply to people who have traveled to the designated areas in the two weeks prior to their attempted entry.

There have been seven confirmed US cases of the 2019 Novel Coronavirus, which originated in a live seafood market in Wuhan, in Hubei province, in December.

The World Health Organization has already declared the epidemic a global emergency, and the Chinese death toll has risen to 259 while total infections reached nearly 12,000, surpassing the SARS epidemic of two decades ago.

Three US airlines, American, Delta and United said they would soon suspend all flights to China.

First federal quarantine in 50 years

Earlier, officials imposed mandatory 14-day quarantine orders on 195 Americans who were air evacuated from Wuhan, the first time a federal directive of this kind was issued for more than 50 years.

The last case involved a person who was evaluated for smallpox in the 1960s.

A plane carrying the repatriated citizens, who include diplomats and their families, touched down at the March Air Reserve Base in Riverside, California, on Wednesday and officials initially said the passengers would be asked to voluntarily isolate themselves for up to 72 hours.

The World Health Organization has already declared the epidemic a global emergency.

Questions over test accuracy

The repatriated group submitted samples for testing at the CDC headquarters in Atlanta -- but officials now say they are not certain about the accuracy of their diagnostic tools.

"We are seeing in the cases that are in the hospital, we've seen people who had detectable virus, and they didn't have the technical virus, and then three days later they had detectable virus," said Robert Redfield, the CDC's director.

Despite the seemingly drastic actions, the US public "should not let fear or panic guide your actions," said senior CDC official Nancy Messonnier, but instead exercise normal precautions for stopping the spread of respiratory viruses.

These include washing your hands thoroughly for at least 20 seconds, disinfecting surfaces, staying home when sick and covering your cough or sneeze with a tissue and then throwing it in the trash.

Agence France-Presse