The Shenzhou XXI mission crew aboard China's Tiangong space station conducted their second spacewalk on Monday, the China Manned Space Agency said.

Mission commander Senior Colonel Zhang Lu and spaceflight engineer Major Wu Fei returned to the Wentian science module at 7:35 pm after spending seven hours outside the orbital station, the agency said in a news release.

The third crew member, payload specialist Zhang Hongzhang, remained inside Tiangong to provide support.

With assistance from ground controllers and the use of a robotic arm, the astronauts completed all assigned tasks, including installing shields designed to protect the station from space debris.

The operation marked the 26th spacewalk carried out by Chinese astronauts.

With the latest outing, Zhang Lu has now completed six spacewalks, joining Senior Colonel Chen Dong in reaching that milestone.

The Shenzhou XXI crew is conducting China's 16th crewed spaceflight and represents the 10th group of astronauts to live aboard Tiangong, currently the only space station independently operated by a single country.

The three astronauts have been aboard the station for more than four months since arriving on Nov 1.

They are scheduled to carry out additional spacewalks before returning to Earth, according to the agency.