New York CNN Business  — 

US airlines are giving customers more time to change their flights to China without incurring fees as the deadly coronavirus continues to spread, and as American authorities raise travel precautions for the country.

American Airlines (AAL) and Delta Air Lines (DAL) on Monday each extended change fee waivers through the end of February. Earlier, they had issued waivers through the end of January.

That means people scheduled to fly before then on either airline to Beijing or Shanghai — the two cities that each company serves in mainland China — can change to a different flight without paying a fee to do so.

United Airlines (UAL) also extended waivers for change fees on flights to Beijing, Shanghai or Chengdu through the end of February. Last week, it offered waivers through February 7.

United is also offering refunds to passengers traveling to Wuhan if they bought their ticket by January 21 and are expected to travel there from now until March 29.

The US Centers for Disease Control and Prevention on Monday raised its travel precaution for China to its highest level. That means it’s advising travelers to “avoid nonessential travel” to the country. Previously, only Hubei province — where Wuhan is located — carried such a warning.

The coronavirus has continued to spread. More than 100 people are dead and more than 4,500 cases have been confirmed in mainland China, according to health officials in the country. Dozens of others have been infected worldwide, including at least five cases in the United States.

The CDC has said it is now monitoring for symptoms of the virus among passengers arriving at 20 US airports.

The agency has also announced enhanced screening of passengers from Wuhan at five airports: John F. Kennedy International Airport in New York, San Francisco International Airport, Los Angeles International Airport, Chicago’s O’Hare International Airport and Hartsfield-Jackson Atlanta International Airport.

On Monday, a health official with the CDC said the agency had screened about 2,400 people so far.

— CNN’s Dave Alsup and Michael Nedelman contributed to this report.