A traveller from China has been diagnosed in Seattle with the Wuhan coronavirus, a spokesman from the US Centers for Disease Control and Prevention has said.
A CDC spokesman has said more details will be released in a news conference later today.
The newly identified coronarvirus originated in the central Chinese city of Wuhan and has spread to Beijing and Shanghai.
More than 300 people have been infected so far and six have died, according to Chinese health officials.
Last week, the CDC began screening travellers from China in three US airports.
Besides the United States, cases outside of China had been reported in South Korea, Thailand, Taiwan and Japan.
Earlier today, Taiwan reported its first confirmed case of the SARS-like coronavirus as the government warned the public against travelling to the Chinese city where it emerged.
The patient is a Taiwanese woman in her 50s, living in Wuhan, who returned to the island yesterday with symptoms including fever, coughing and a sore throat.
Asian countries have stepped up measures to block the spread of the new virus as the death toll in China rose to six and the number of cases jumped to almost 300 since it first emerged in Wuhan.
The Taiwan patient reported her symptoms to quarantine officials on arrival at Taoyuan airport and was immediately taken to a hospital for treatment, said the island's Centers for Disease Control (CDC).
The woman told officials that she had not visited any local markets or had contact with birds or wild animals while in Wuhan.
Authorities are monitoring some 46 passengers and crew from the same flight, the agency said.
The CDC raised its alert on Wuhan to the highest level, urging the public against travelling to the city unless necessary.
"We ask the public not to panic as the individual was taken to hospital directly from the airport and did not step into the community," it said in a statement, adding that it reported the case to the World Health Organization and China authorities.
The World Health Organization said that the new coronavirus was likely to spread to other parts of China and possibly other countries in the coming days.
So far in China, the virus has mostly been concentrated in Wuhan city, although isolated cases have also been reported in Shanghai and Beijing, while health authorities in Henan province have confirmed the first case of coronavirus there.
Meanwhile, Russian airports have stepped up screening of travellers arriving from China to try to identify people infected with the new coronavirus, according to airport officials.
At least four airports, Sheremetyevo and Vnukovo in Moscow, as well as airports in Yekaterinburg and Irkutsk, have introduced screening measures to try to identify infected passengers, Russian airport officials said.
Russia's consumer health regulator, Rospotrebnadzor, said it could not rule out the possibility that the infection could spread to Russia, but evaluated the risk of a widespread outbreak in Russia as low, the Interfax news agency reported.
It said a testing system to diagnose the new coronavirus had already been developed in Russia and that laboratories would start receiving it by the end of the week, Interfax reported.