The Shenzhou XXI crew aboard China's Tiangong space station conducted their first spacewalk on Tuesday, according to the China Manned Space Agency.

Mission commander Senior Colonel Zhang Lu and spaceflight engineer Major Wu Fei returned to the Wentian science module at 6:45 pm after working for approximately eight hours outside the orbital outpost, the agency said.

Payload specialist Zhang Hongzhang, the third member of the Shenzhou XXI mission, stayed inside Tiangong to provide support.

Assisted by a team on Earth and the space station's robotic arm, the astronauts completed all assigned extravehicular tasks, including installing space debris shields and replacing old instruments with new ones.

They also checked and photographed the windows of the Shenzhou XX spaceship's reentry capsule, one of which was damaged by a tiny piece of space debris, leading to the delayed return of the Shenzhou XX crew, the agency said.

This was the 25th spacewalk carried out by Chinese astronauts. Wu, 32, became the youngest Chinese astronaut to carry out extravehicular activities to date. The record was earlier held by Lieutenant Colonel Tang Shengjie, who made his first spacewalk at age 34.

The Shenzhou XXI astronauts are conducting China's 16th manned spaceflight and comprise the 10th group of residents aboard Tiangong, which is currently the only operational space station independently run by a single nation.

The three astronauts have been aboard the colossal orbital outpost for nearly 40 days since arriving on Nov 1. They have examined instruments and carried out necessary maintenance work, checked emergency-response materials, and conducted emergency drills and robotic arm training.

The crew members will conduct additional spacewalks and scientific tasks and, if necessary and feasible, they may also repair the broken viewport window on the Shenzhou XX spacecraft, the agency said.