The China National Offshore Oil Corporation (CNOOC) has discovered an oilfield in the South China Sea with proven reserves exceeding 100 million tonnes, Xinhua news agency reported on Monday.

The newly found Huizhou 19-6 oilfield is not in a disputed part of the South China Sea and lies within China's Exclusive Economic Zone, which runs for 200 nautical miles or 370 km from its coast.

The oilfield, around 170 km (106 miles) off the coast of Shenzhen, sits at an average water depth of 100 metres, the report said, adding that test drilling has yielded a daily production of 413 barrels of crude oil and 68,000 cubic metres of natural gas.

Huizhou 19-6 is China's first large-scale integrated clastic oilfield in the deep to ultra-deep layers, the report said.

Such reserves are challenging for oil and gas exploration, given the high temperatures and pressures exerted at these depths.

China wants to reduce its import dependency to bolster its energy security, but its crude oil imports are expected to peak as early as next year as transport fuel demand begins to decline for the world's top oil buyer.