Delta Air Lines Inc. service to China "remains very fluid” after a flight to Shanghai from the U.S. was turned back because of procedures needed to clean and disinfect the airplane, the carrier said.

The flight returned to Seattle in order "to be compliant with cleaning mandates required at Shanghai Pudong International Airport that were issued by the Chinese government on Dec. 21,” Delta said in a statement.

The requirements, which would have significantly extended ground time, are "not operationally viable,” the airline added. The changes were announced the same day the Delta flight reversed course.