A weaker yuan crushed the first-half net profits of China's three largest airlines, statements from the carriers show.

China Eastern Airlines Co Ltd on July 18 estimated that its net profit would be no more than 50 million yuan ($8.06 million) in the first six months, compared with 763 million yuan a year earlier.

Air China Co Ltd, the flag carrier, warned of a profit decline of 55 to 65 percent in the first half of 2014, according to a statement on July 14.