Two astronauts made the first space walk on Sunday outside China's new orbital station to work on setting up a 15-meter (50-foot) long robotic arm.
Liu Boming and Tang Hongbo were shown by state TV climbing out of the airlock as Earth rolled past below them. The third crew member, commander Nie Haisheng, stayed inside.
The astronauts arrived June 17 for a three-month mission aboard China's third orbital station, part of an ambitious space program that landed a robot rover on Mars in May. Their mission comes as the ruling Communist Party celebrates the 100th anniversary of its founding.
The station's first module, Tianhe, or Heavenly Harmony, was launched April 29. That was followed by an automated spacecraft with food and fuel. Liu, Nie and Tang arrived June 17 aboard a Shenzhou capsule.
On Sunday, Liu and Tang were completing installation of a robotic arm that will be used to assemble the rest of the station, according to state media. State TV said their space suits are designed to allow them to work in the vacuum of space for up to six hours if needed.
The space agency plans a total of 11 launches through the end of next year to add two more modules to the 70-ton station.
Liu is a veteran of the Shenzhou 7 mission in 2008, during which Zhai Zhigang made China's first space walk. Nie is on his third trip into space while Liu is making his first. All are military pilots.
This is China's first crewed mission in nearly five years, according to an AFP report. China's ambition to build an orbiting outpost of its own was fuelled in part by a US ban on its astronauts on the International Space Station, a collaboration between the United States, Russia, Canada, Europe and Japan, the report adds.
The International Space Station is due for retirement after 2024, although Nasa has said it could potentially remain functional beyond 2028. Tiangong is expected to have a lifespan of at least 10 years, and China has said it would be open to international collaboration on the station, the AFP report explains.
(With inputs from AP and AFP)