A manned Chinese submersible broke through the 7,000-metre mark for a new national deep water dive record on Sunday, state media said, as the Asian giant showed off its technological might.

The "Jiaolong" craft reached 7,020 metres (23,031 feet) in the Mariana Trench in the western Pacific Ocean on its fourth dive since arriving in the area earlier this month, state television said.

The dive came on the same day China successfully completed its first manual space docking, a complex manoeuvre that will bring the country a step closer to building a space station.

"This (dive) shows the performance of the submersible is stable," mission chief commander Liu Feng told a live television broadcast from 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 men into the Mariana Trench, the deepest place in the world, then returned to the choppy surface after nearly 11 hours.

The same submersible reached 5,188 metres in a Pacific dive in July last year. And in a series of three previous dives since June 15, the craft has gone deeper still. Experts say 7,000 metres is the limit of its design.

Other manned submersibles have gone deeper than China's craft. 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.

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, experts say.

On its third dive on Friday, the crew collected samples of water and sediment and took photos of sea life, the official Xinhua News Agency said.

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.

And the stability and durability of the craft presents further difficulties for future operations.

The recent round of dives have seen some technical glitches, such as the breakdown of communications equipment and problems with the adjustable ballast system, state media has reported.

The 7,000 metre dive was previously scheduled for Monday, state media had reported. The reasons for the change of date were unclear but mean the record-setting dive came the same day as China's landmark space manoeuvre.