Preparations had begun for the launch of Long March 5B, a rocket carrying the core module for the construction of China’s space station.
Police restricted traffic near the Wenchuan space port between Wednesday and Thursday evening, an indication that the launch window might occur during that time.
U.S. experts expect a Thursday take-off for the Long March 5B rocket, which has been on the launch pad at Wenchuan on the southern Chinese island of Hainan since the weekend.
But the exact date is still unconfirmed.
The rocket will carry the Tianhe (Heavenly Harmony) core module for the space station Tiangong (Heaven’s Palace), which is due to be completed around 2022.
Two further fights are to follow in close succession in May and June, U.S. experts said.
It would be the second permanent outpost in space after the International Space Station (ISS).
If the ISS were to cease service as planned in 2024, China would become the only nation to operate a space station.
Tianhe is 16.6 metres long with a diameter of 4.2 metres.
The core module provides electricity and propulsion and has accommodation for three astronauts to stay on board for up to six months.
Two other parts will be attached to form a T shape.
At around 90 tons, the Tiangong space station will be much smaller than the 240-ton ISS. (dpa/NAN)