The US Centers for Disease Control and Prevention (CDC) is advising Americans to avoid nonessential travel to China and has established screening protocols at 20 US airports to combat the spread of coronavirus.

US-based airlines are responding to the CDC directive by offering free flight changes on China itineraries for at least the next month.

The CDC said January 28 that there are now five confirmed cases of 2019 Novel Coronavirus (2019-nCoV) in the US, with the latest travel-related cases discovered in Arizona and California. Previous cases were in Washington and Illinois.

The Associated Press reported that the 20 airports screening passengers for the coronavirus, which originated in Wuhan, China, account for 90 per cent of all US-bound Chinese air travellers.

Ports with screening and quarantines in effect include Los Angeles, San Francisco, San Diego, Seattle, Anchorage, Honolulu, Boston, New York, Philadelphia, Washington, Atlanta, Miami and Houston.

Both Delta Air Lines and United Airlines have extended their change-fee waivers on China flights through the end of February, according to CNN Business.

In China, the 2019-nCoV virus has already killed more than 100 people and infected 4,500.