A suspected strike by "tiny space debris" has delayed the return of the Chinese spaceship Shenzhou-20 and three astronauts, Beijing's space agency said on Wednesday.

"The Shenzhou-20 manned spacecraft is suspected of being hit by a tiny piece of space debris, and an impact analysis and risk assessment are under way," the China Manned Space Agency (CMSA) said in a statement.

The return of the spacecraft and the three astronauts, planned for Wednesday, has been postponed to ensure their safety, the statement said.

Chen Dong, Chen Zhongrui and Wang Jie had been expected to touch down at the Dongfeng landing site in northern Inner Mongolia. The CMSA did not give a new date for their return.

A relief crew arrived at the Tiangong space station aboard the Shenzhou-21 last week.