The latest drop takes the fall since the contract's launch on Monday to 10 percent.
Volume in the overnight session from 9 p.m. to 2:30 a.m. in China was healthy with more than 50,000 lots, equal to 25 million barrels of oil trading.
Shanghai crude oil futures were down 1.7 percent at 407.1 yuan ($64.67) per barrel at 9:09 a.m. (0109 GMT). ($1 = 6.2946 Chinese yuan renminbi)