The return of the Shenzhou XX crew from the Tiangong space station, originally set for Wednesday, has been postponed due to safety concerns linked to space debris, according to the China Manned Space Agency.

The agency said in a short news release on Wednesday morning that the decision was made after learning that the Shenzhou XX spacecraft, which is tasked with bringing the three crew members back to Earth, was at risk of being hit by tiny debris.

"The analysis of the impact's effects and risk assessment are underway. To ensure the astronauts' safety and the mission's success, it has been decided that the Shenzhou XX crew's return flight will be postponed," it explained, without disclosing the new date for the return trip.

The Shenzhou XX team — mission commander Senior Colonel Chen Dong and crew members Colonel Chen Zhongrui and Colonel Wang Jie — have been aboard the Chinese space station for more than six months since their arrival on April 25.

They represent China's 15th manned spaceflight and are the ninth group of residents aboard the Tiangong, which is currently the only operational space station independently run by a single nation.

Their successors — three astronauts in the Shenzhou XXI mission — arrived at the colossal orbital outpost on Saturday and have taken control of station operations.