President Xi Jinping has called for China to establish itself as a space power, and it has tested anti-satellite missiles, in addition to its civilian aims.

China says its space program is for peaceful purposes, but the US Defense Department has highlighted its increasing capabilities, saying it was pursuing activities aimed to prevent adversaries from using space-based assets in a crisis.

"The astronaut flight group is in good condition, pre-launch preparations are basically ready," space program official Wu Ping told reporters at a briefing.

After Monday's launch at 2330 GMT, the astronauts will dock with the Tiangong 2 space laboratory, where they will spend about a month, testing systems and processes for space stays and refuelling, and doing scientific experiments.

China launched Tiangong 2, its second experimental space lab, last month.