Chinese airlines ordered more than $US100 billion of planes from Airbus and Boeing in the past decade. Paying those bills is getting harder with the trade war pushing the local currency to its weakest level in six months.

Air China, China Southern Airlines and other carriers will need to pay more for new aircraft, which are always priced in dollars. The airlines also need to spend in foreign currency for fuel purchased overseas, which is somewhat cushioned by international ticket sales. All told, the carriers are bracing for more expenses and fewer passengers as trade tensions build up between the world's two biggest economies.

Investors have pummeled the shares of the country's three biggest carriers on concern the weaker yuan will result in a dip in earnings. Shares in flag-carrier Air China have tumbled 20 per cent in Hong Kong since June 13, while China Southern Airlines and China Eastern Airlines have slid 23 per cent and 17 per cent, respectively, since June 14, losing a combined market value of about $US11.5 billion.

Shares in flag-carrier Air China have tumbled 20 per cent in Hong Kong since June 13. Joseph Nair

"Trade concern is the one that's pushing the yuan down," said Mohshin Aziz, an aviation analyst at Maybank Investment Bank in Kuala Lumpur. "That's the root cause of all the branches of troubles we're going through."

A weaker yuan also means higher interest payments on dollar-denominated debt. Air China had about $US21 billion of dollar-denominated debt; China Southern had $US18 billion; and China Eastern $US11 billion, according to data compiled by Bloomberg.