A manned Chinese submersible broke through the 7,000-metre mark in an ocean dive on Sunday, state media said, setting a new national record for China.
The "Jiaolong" craft dived 7,015 metres (23,015 feet) in the Mariana Trench in the western Pacific Ocean on its fourth dive since arriving in the area earlier this month, the official Xinhua news agency said.
"This shows the performance of the submersible is stable," mission chief commander Liu Feng told state television aboard the ship supporting the submersible.
"The level of our technical personnel is getting better and better."
The Jiaolong -- named after a dragon from Chinese mythology -- carried three people deep into the Mariana Trench, the deepest place in the world.
The same vessel reached 5,188 metres in a Pacific dive in July last year. But in a series of three previous dives since June 15, the craft has gone deeper each time.
Experts say China intends to use the submersible for scientific research, such as collecting samples of undersea life and studying geological structures, as well as future development of mineral resources.
Scientists say the ocean floors contain rich deposits of potentially valuable minerals, but the extreme depths pose technical difficulties in harvesting them on a large scale.
Earlier this year, American film director James Cameron descended almost 11,000 metres to the bottom of the Mariana Trench.
His effort is believed to have at least equalled the record for the deepest manned dive, set by a US Navy officer and a Swiss oceanographer in 1960, according to Guinness World Records.