Chinese astronauts onboard the nation's Tiangong space station entered the Mengtian lab module on Thursday afternoon, several hours after the completion of the station's in-orbit assembly.

Crew members of the Shenzhou XIV mission — mission commander Senior Colonel Chen Dong, Senior Colonel Liu Yang and Senior Colonel Cai Xuzhe — opened Mengtian's hatch and entered the lab component at 3:12 pm, about six hours after the lab carried out a crucial transpositioning operation.

Chen and his crewmates have been living inside Tiangong for nearly five months.

The China Manned Space Agency said in a news release in the coming weeks, the Shenzhou XIV crew will welcome the arrival of the Tianzhou 5 robotic cargo ship and the Shenzhou XV manned spacecraft, which will bring another three-astronaut team with them in making the first in-orbit crew shift.

On Thursday morning, Mengtian was moved from an axial port of the Tiangong station's Tianhe core module to a radial port on the core module in an hour-long transpositioning operation that finished at 9:32 am.

After the operation, the Tiangong station has taken on a T shape and will remain in that shape for the next several years, the agency noted, adding function checks and assessments will be carried out in the coming days.

Mengtian, the third major component of the Tiangong space station and its second lab module, was launched on Monday afternoon by a Long March 5B heavy-lift rocket from the Wenchang Space Launch Center in Hainan province.

The module is about 17.9 meters long, has a diameter of 4.2 meters and weighs more than 23 metric tons. It has 32 cubic meters of inner space that can be used by astronauts, according to its designers at the Shanghai Academy of Spaceflight Technology.

The spacecraft consists of four sections — a crew working compartment, a payload section, an airlock cabin and a service module.