The Long March-5B carrier rocket took off at 1800 local time (1000 GMT) at the Wenchang Space Launch Center in the southern island province of Hainan.
China's largest carrier rocket is carrying a new-generation spacecraft, state broadcaster CCTV said.
It was the first mission carried out by the Long March-5B, CCTV reported.
The Long March-5B - with a length of about 53.7 metres and takeoff mass of about 849 tonnes - was also carrying an inflatable cargo return module.
China said in March it was aiming to launch an experimental spacecraft without a crew as part of a broader spaceflight program to shuttle astronauts to its future space station and for future manned space exploration.
The launch was earlier scheduled for mid- to late April.
China has since been racing to catch up with Russia and the United States to become a major space power by 2030.
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