Delta Air Lines announced Wednesday that it was reducing the frequency of its flights to China to 21 from 42 per week.

The airlines are allowing passengers who were planning to travel to, from or through Beijing or Shanghai, and in some cases Chengdu, to rebook their itineraries without a change fee, though the policies differ and passengers are advised to contact their carrier.

Delta Air Lines said that no refunds would be issued and that rebooked travel must begin before May 31 to avoid change fees and the difference in fare; after that date, the change fee will be waived but passengers will be assessed any applicable difference in fare. Passengers may cancel their itineraries in exchange for a travel credit (but with payment of any difference in fare and the applicable change fee).

American Airlines will permit travelers to delay their trips for up to one year from the original ticket date without change fees (but with payment of any difference in fare). Refunds are offered only for flights to Wuhan. Emirates passengers may request a refund if they no longer wish to travel to Shanghai, Beijing or Guangzhou (for travel up to Feb. 6) or change their travel dates (for travel up to Feb. 29).

United will allow passengers to rebook without penalty (but with payment of any difference in fare) for trips after March 31.

Cathay Pacific, the Hong Kong-based carrier, and Cathay Dragon, its regional subsidiary which operates in mainland China, are permitting passengers to rebook or reroute flights without charge to mainland China, so long as passengers travel on or before May 31. The airline has announced that it is reducing its number of flights to mainland China by up to half.

In a first since the SARS crisis in 2002 and 2003, Cathay Pacific is permitting its crew and staff to wear surgical masks at work, and has announced in-flight service changes such as eliminating hot towels, pillows, blankets and magazines. Likewise, American Airlines: “While it is not medically recommended, American will allow flight attendants to wear masks on flights to and from Shanghai, Beijing and Hong Kong,” said Curtis Blessing, an American spokesman, in a statement. The masks are ubiquitous across Asia, but not common in North America.