The United States has confirmed the first case of the new coronavirus on its territory.
The Centers for Disease Control said the virus, which originated in China, had been diagnosed in a US resident who arrived in Seattle from China.The virus, which spread from the Chinese city of Wuhan, has infected almost 300 people, and six have died.
North Korea has temporarily closed its borders to foreign tourists in response to the threat, a tour operator says.
The patient diagnosed in the US - reported to be a man in his 30s - returned from Wuhan on 15 January, the CDC said.
"The patient sought care at a medical facility in the state of Washington, where the patient was treated for the illness," it added in a statement.
"Based on the patient's travel history and symptoms, healthcare professionals suspected this new coronavirus."
Laboratory testing of a clinical specimen confirmed the diagnosis on 20 January, the CDC statement continued.The announcement that North Korea was barring entry to foreign tourists came from Young Pioneer Tours, which is based in China and specialises in travel to North Korea.
The company said in a statement that North Korea was implementing a temporary ban as a precaution.
"Further details are yet to be confirmed by our travel partners in North Korea and we will continue to make all future announcements on our website," Young Pioneer Tours said.
Another tour group that travels to North Korea, Koryo Tours, also tweeted about "possible limits to tourist entry".
Some experts have previously warned that international sanctions on North Korea had hit the country's healthcare system, by restricting the delivery of aid and medical equipment.
Last November, US doctor Kee B Park wrote in USA Today: "I have seen how the North Korean doctors have adapted to scarcity. For example, they reuse intravenous catheters, scalpels, gauze and gloves by meticulously cleaning and re-sterilising them - until they become unusable."