China's crude oil processing volume in August inched up 1.5 percent year-on-year to 37.7 million tons, the National Bureau of Statistics (NBS) said on Tuesday.

Crude processing volumes rose in the previous two months after falling on an annual basis between April and June, but the gains have been small. Gasoline output rose 5.8 percent year-on-year to 7.47 million tons in August while diesel production fell 0.5 percent from a year earlier to 13.74 million tons, the third decline in 2012.

"Refiners were still cautious about raising their operating rates in August as demand stayed weak amid uncertainties over China's economy," Dong Lizhu, an oil analyst, told Interfax on Thursday. A purchasing managers index for manufacturing published by the NBS fell below the 50 line that demarcates expansion from contraction for the first time in nine months in August and a separate index compiled by HSBC for the same month fell to 47.6, the lowest level since March 2009.

China lifted retail fuel prices on Aug. 10 but an anticipated increase in output at refineries operated by Shanghai and Hong Kong Stock Exchange-listed PetroChina Ltd. and Sinopec Corp. did not materialise. The average operating rate of the two firms' refineries in August was 81 percent, down one percent from a month earlier, said Dong.

Operating rates at private refineries, located mostly in north China's Shandong Province, rose seven percent on a monthly basis in August to 36 percent, however, those facilities account for less than 20 percent of total crude oil processing, noted Dong.

Crude oil imports in August fell 12.55 percent on an annual basis to 18.4 million tons, according to preliminary data released by the General Administration of Customs, reflecting the hesitation among refineries about ramping up production too soon.

The National Development and Reform Commission on Tuesday raised the per ton price of gasoline by RMB 550 ($87) and diesel by RMB 540 ($85) following a surge in global crude oil prices.