China's daily crude oil imports fell in May, after reaching a record high in April, as refining capacity dropped the most this year due to maintenance.

Net overseas purchases were 26.08 million tonnes, according to data released by the general administration of customs in Beijing at the weekend.

That's about 6.17 million barrels a day, declining from a record 6.81 million in April.

Crude-processing capacity in China, the world's second-largest oil consumer, dropped 3.93 million tonnes in May, the sharpest plunge this year, according to ICIS-C1, a commodities researcher based in Shanghai.

The decline was even greater than in April, when capacity fell 3.1 million tonnes as more than 80 of the nation's biggest refineries were taken offline.

Plants in China typically do maintenance in the second quarter before fuel consumption peaks during the northern summer.

PetroChina Company halted the Dalian refinery, its largest by capacity at 20 million tonnes a year, from April 10 to May 24 for seasonal repairs. China Petroleum & Chemical Corporation, known as Sinopec, closed the 11.5 million-tonne Changling plant from March 18 to May 15 and is carrying out upgrading and expansion work at its 8 million-tonne Shijiazhuang facility between April and July.