BEIJING -The module, named "Tianhe", or "Harmony of the Heavens", was launched on the Long March 5B, China's largest carrier rocket, at 11:23 a.m. (0323 GMT) from the Wenchang Space Launch Centre on the southern island of Hainan.
Tianhe is one of three main components of what would be China's first self-developed space station, rivalling the only other station in service - the International Space Station (ISS).
The ISS is backed by major countries including the United States, Russia and Japan. China was barred from participating in the ISS by the United States.
Tianhe will form the main living quarters for three crew members in the Chinese space station, which will have a life span of at least 10 years.
The Tianhe launch was the first of 11 missions needed to complete the space station, which will orbit Earth at an altitude of 340 to 450 kilometres (211-280 miles).
In the later missions, China will launch the two other core modules, four manned spacecraft and four cargo spacecraft.
Work on the space station programme began a decade ago with the launch of a space lab Tiangong-1 in 2011, and later, Tiangong-2 in 2016.
Both helped China test the programme's space rendezvous and docking capabilities.
China has prioritised space exploration in recent years, with the aim of becoming a major space power by 2030.
By 2045, it hopes to establish a programme operating thousands of space flights a year and carrying tens of thousands of tonnes of cargo and passengers.
(Reporting by Ryan Woo and Liangping Gao; Editing by Christian Schmollinger & Simon Cameron-Moore)