China's net exports of diesel rose to the highest level in 18 months in September, as the nation raised its daily oil processing to a record high.

Net exports, or overseas sales minus imports, climbed to 167,689 metric tons, the most since March 2011, according to customs data released on Wednesday.

China processed 9.47 million barrels a day of crude last month, 7 percent more than a year earlier and the most ever on a daily basis.

C1 Energy, a Shanghai-based commodity researcher, said the country may raise diesel exports to as much as 400,000 tons in October as production outpaces domestic demand, and refiners will probably get additional export quotas from the government.

Diesel exports last month hit 170,227 tons, while imports fell 99 percent from a year earlier to 2,538 tons, the data showed.

Gasoline exports were at 288,019 tons, the highest since March. Liquefied natural gas imports rose 20 percent to 1.38 million tons, and coal imports, including lignite, dropped 18.6 percent to 18.63 million tons.