SHANGHAI - A Chinese deep-sea explorer ship, Zhang Jian, set sail on Tuesday from Shanghai to the South Pacific for scientific research.

The vessel is the mother ship of the 11,000-meter Rainbow Fish submersible, which Chinese researchers are preparing to send to the Mariana Trench late this year or early next year, said Fang Jiasong, chief scientist of the mission.

During the two-month journey, scientists will test the navigation abilities of the ship and its scientific equipment, said Fang. The ship carries the landing device for the Rainbow Fish submersible, he added.

Its destination is the waters of the New Britain Trench, which is more than 8,000 meters deep in the Solomon Sea off Papua New Guinea, he said.

"The journey is an important step in our efforts to take on the Mariana Trench," said Fang.

The ship, named after the founder of Shanghai Ocean University, is 97 meters long and 17.8 meters wide. It has a designed displacement of around 4,800 tonnes and an endurance of 15,000 nautical miles.

It will be used for general ocean expedition missions, deep-sea engineering, rescue and salvage, underwater archaeology and film shooting.

China began developing Rainbow Fish in 2014. It will be able to go much deeper than the Jiaolong submersible, which set a Chinese record for manned diving when it reached 7,062 meters in the Mariana Trench in June 2012.

With a combined area larger than the United States, the world's 26 hadal trenches, at depths of 6,500 meters or more, are home to many unknown species as well as energy and metal resources. Explorations at these depths have been held back by difficulties including high pressure and low temperatures.