A manned Chinese submersible set a new record for the country's deepest sea dive Friday, over 6,000 metres, showing Beijing's technological ambitions as it also readies for its first manned space docking.

The "Jiaolong" craft dived over 19,685 feet into the Mariana Trench in the western Pacific Ocean, the first in a series of six dives which will plumb depths of 7,000 metres, the official Xinhua news agency said.

The deep-sea dive push comes as China prepares to launch a spacecraft on Saturday to conduct its first manned space docking, as part of efforts to establish a permanent space station by 2020.

The submersible, which carried three men, reached around 6,500 metres with only a technical glitch in communications, state media said.

"In our first battle, we have already reached 6,500 metres. All of our tasks have been completed," chief commander Liu Feng told state television aboard the ship carrying the submersible.

He said a piece of communications equipment on the surface of the water failed, but the team switched to a back-up system and restored communications. He did not say whether contact was completely lost with the Jiaolong.

The same vessel -- named after a dragon from Chinese mythology -- reached 5,188 metres in a Pacific dive last July, the nation's previous record.

Friday's dive sparked outpourings of nationalism on the Internet and comparisons to the upcoming space launch.

"Three pilots will take the Jiaolong to attempt the 7,000-metre dive, while three astronauts will take the Shenzhou-9 to connect with the Heavenly Palace," a Shanghai based blogger wrote on his microblog.

"Up in the sky we can pluck the moon, down in the oceans we can catch the turtles," said the posting on Sina's microblog service, quoting a saying attributed to late Chinese leader Mao Zedong.

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.

But one Chinese expert on Friday described the latest dives as an "experiment" for China and said future use of submersibles for scientific research faced obstacles, such as with stability and durability of the craft.

"Even after it reaches the 7,000-metre depth, it still remains a question whether it can achieve scientific purposes," Zhou Huaiyang, professor of the School of Ocean and Earth Sciences at Shanghai's Tongji University, told AFP.

Scientists say the oceans' 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 -- the deepest place in the world.

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.