Reliance Industries, owner of the world's biggest refining complex, said on Friday it plans to shut one of its crude units and a coker at its first refinery for three to four weeks, leading to about 19% less crude processing at the complex.

Reliance's Jamnagar complex comprises a 600,000 bpd old refinery and a 580,000 bpd export focused plant, which was commissioned in end-2008.

The shutdown of crude distillation unit I and coker at the 660,000 bpd refinery would start in the last week of October and was expected to last three to four weeks, Reliance said in a stock exchange filing, confirming earlier Reuters reports.

The refinery has two crude units of about 330,000 bpd each and a 160,000 bpd delayed coker.

"The last maintenance and inspection for these units were carried out in October 2005," it said.

The company said during the shut down period the Jamnagar complex will process about a million bpd of crude, about 19% less than installed capacity of 1.24 million bpd. It said the rest of the units at the two plants would continue to operate at normal levels.