Two astronauts made the first space walk outside China's new orbital station on Sunday to work on setting up a 15-meter 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, which is part of an ambitious space program that landed a robot rover on Mars in May.
The robotic arm 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.
Their mission comes as the ruling Communist Party celebrates the 100th anniversary of its founding.