Shenzhou XIII mission crew members have started to transfer supplies from the Tianzhou 2 and 3 robotic spaceships to the Tiangong space station, in preparation for their six-month stay inside the orbiting core module.

Mission commander Major General Zhai Zhigang, Senior Colonel Wang Yaping and Senior Colonel Ye Guangfu opened Tianzhou 3's hatch at 9:50 am on Sunday and then floated into the craft, the China Manned Space Agency said in a brief statement on Sunday morning.

The crew entered Tianzhou 2 on Sunday afternoon after a midday break, sources close to the mission said.

They checked the packages inside the cargo ships and moved some necessities to the core module, Tianhe, or Harmony of Heavens. The crew members also installed some crucial living devices inside Tianhe, according to the sources.

Feng Yong, project manager of Tianzhou 3 at the China Academy of Space Technology in Beijing, said the unmanned craft is carrying equipment required for a spacewalk, maintenance apparatus, spare parts, experimental material, emergency-response materials as well as necessities such as drinking water, compressed oxygen and hygiene kits. These supplies are enough for the astronauts' six-month stay, he added.

In addition, the spacecraft has propellants to refuel Tianhe. It can also generate and supply electricity to the core module. Seeds to grow plants and vegetables are also inside Tianzhou 3 for mutation breeding experiments, according to the engineer.

The Shenzhou XIII spacecraft was lifted into space by a Long March 2F carrier rocket early on Saturday morning from the Jiuquan Satellite Launch Center in northwestern China's Gobi Desert. It is the fourth spacecraft to dock with the Tiangong station and the second crewed mission to the orbiting craft.

The mission crew entered Tianhe on Saturday morning, embarking on what is expected to become the country's longest spaceflight.

Before setting out for the flight, Zhai told China Central Television that he packed Chinese writing brushes, paper and an ink stone inside his luggage, hoping to practice Chinese calligraphy in his spare time. He also brought a lot of recordings of TV programs and music to enjoy during the stay, according to the State broadcaster.

Wang, the female member of the crew, told CCTV that she plans to play a musical instrument and display articles that represent Chinese cultural elements during her video calls with members of the public.