The first deep-sea exploration vessel designed in China has completed a geological examination in the Pacific.

The research vessel "Hang Yang Liu Hao" (Ocean No. 6) returned to port in southern China's Guangdong Province on Sunday after 138 days of deep-sea surveys, according to Yang Shengxiong, chief engineer with the Guangzhou Marine Geological Survey.

The surveys over nearly 30,000 km were conducted in areas with cobalt-bearing crusts in the Western Pacific Ocean to determine the conditions of the crusts in more than 30 areas, Yang said.

"Samples of the crusts more than 30-cm thick were fetched for the first time," the official said.

The vessel also realized scale collection of cobalt-bearing crusts and collected samples of microplastics. It also analyzed the amount, types and composition of microplastics in the sea, laying a foundation for international treatment of marine plastic waste.

It is the eighth deep-sea expedition of the vessel, which has conducted multiple tasks in the South China Sea, the Pacific and the waters around the Antarctic since 2009.

(Top image: China's first self-designed research vessel Ocean No.6 returned to port after completing a deep-sea geological examination in the Pacific. /VCG Photo)