China's manned deep-sea submersible, the Jiaolong, reached a depth of 6,965 meters below sea level on Tuesday during its second dive into the Mariana Trench, surpassing a fresh national record set earlier in the day.

The vessel sat on the sea bed and started working at that depth.

This was the second sit-on-bottom for Tuesday's dive. The previous one reached a depth of 6,908 meters below sea level, where sea drivers collected water samples and placed markers.

The dive, which began at 7 a.m. local time (2100 GMT Monday) after the leaking oil pipe of its hydraulic system had been repaired, is expected to re-check the hydraulic system and test various functions and the security of the submersible at great depths.

Last Friday, the vessel reached 6,671 meters below sea level in the first dive, well surpassing the previous record of 5,188 meters made last July.

The Jiaolong will attempt four more dives, aiming to move deeper and deeper to pursue the goal of reaching 7,000 meters below the sea level between mid-June and early July.

The Xiangyanghong 09, the vessel's oceanographic mother ship, reached the designated dive zone in the Mariana Trench on June 11.