The Tiangong space station is to be the third orbiting laboratory launched and operated by China, following the Tiangong-2 station launched in 2016 and de-orbited in 2019, and Tiangong-1 station that launched in 2011 and ceased operation in 2016.
The mission will be China's longest crewed space mission to date and the first in almost five years, as Beijing pushes forward with its ambitious programme to establish itself as a space power.
The Shenzhou-12 crew is to live on the Tianhe, which means "Harmony of the Heavens", a cylinder 16.6 m (55 ft) long and 4.2 m (14 ft) in diameter, for three months.
A Long March 2F rocket transporting the Shenzhou-12, or "Divine Vessel", bound for the space station module Tianhe blasted off at 9:22am Beijing time (01:22 GMT) from the Jiuquan Satellite Launch Centre in northwestern Gansu province.
Chinese astronauts, from left, Tang Hongbo, Liu Boming, and Nie Haisheng wave as they prepare to board for liftoff in China on Thursday.
To prepare for the mission, the crew has undergone more than 6,000 hours of training.
Nie, 56, a former air force pilot, will be the oldest Chinese astronaut to go to space.
The two other members are also members of the military.
Asked what he would pack for the long trip, Nie - speaking to reporters from behind a glass wall to keep the astronauts quarantined - said his bag was full of "things for entertainment and for hosting mini get-togethers".
Outer space is a shared asset of all people on Earth, and space exploration is a universal cause for humankind, said Ji, adding that China is open to cooperation and exchanges with all nations and regions around the globe that are dedicated to the peaceful use of outer space.
The Shenzhou-12 spacecraft will dock with the Tianhe main section of the space station, which was placed in orbit on April 29.
China's space station construction plan calls for a dozen launches, four of them crewed, stretching into 2022.
The astronauts will be kept busy testing and maintaining the systems onboard, conducting spacewalks and undertaking scientific experiments.
After that they will move, assemble and test extravehicular spacesuits and perform two extravehicular activities for work including assembling an extravehicular toolbox, lifting the panoramic camera and installing extended pump sets.
China's space launches drew intense global attention last month after remnants of the rocket that carried the Tianhe module into space fell back to Earth with no official forecast of their expected landing location until literally the final minutes.
The ISS - a collaboration between the US, Russia, Canada, Europe and Japan - is due for retirement after 2024, although NASA has said it could potentially remain functional beyond 2028.