China will lift jet fuel surcharges for the second time in a year on domestic flights to help air carriers cope with the impact of soaring oil prices.

Starting from September 1, the surcharge for each passenger flying less than 800 kilometres will rise to 60 yuan (US$7.5) from the current 30 yuan (US$3.7), the General Administration of Civil Aviation of China (CAAC), the industry regulator, said on on Friday.

Those flying further will pay a 100 yuan (US$12.5) surcharge, up from 60 yuan, it said.

The move came as the price of aviation fuel has risen 50 per cent since March to more than 5,800 yuan (US$725) per ton.

Mainland airlines posted a combined loss of around 2.5 billion yuan (US$310 million) in the first half of this year, largely due to surging fuel prices, the CAAC said last month. The losses were more than quadruple those in the same period last year.

China Southern Airlines, the country's largest carrier by fleet size, reported a net loss of 835 million yuan (US$104.4 million) for the first half of this year, about level with the loss incurred a year earlier.

Shanghai Airlines posted a net loss of 163.27 million yuan (US$20.4 million) in the first half, compared with a 13.35 million yuan (US$1.66 million) profit last year.

Crude oil prices in the international market have been over US$70 for weeks.

Prices are expected to continue to rise this year, analysts say. High oil prices and the impact of a traditionally slow season for travel in the fourth quarter will hurt airlines' profitability in the second half of the year, they said.

"Given rising fuel prices, it is reasonable that the government allows airlines to increase fuel surcharges to protect the aviation industry," an official said.