China launched a lunar probe on Saturday which is expected to make the first-ever soft landing on the far side of the moon.

A Long March-3B rocket, carrying the Chang'e-4 probe including a lander and a rover, blasted off from the Xichang Satellite Launch Centre in Sichuan province at 2.23 a.m., reports Xinhua news agency.

Since the moon's revolution cycle is the same as its rotation cycle, the same side always faces the earth. 

The other face, most of which cannot be seen from earth, is called the far side or dark side, not because it's dark, but because most of it remains unknown.

The Chang'e-4 mission will be a key step in revealing the mysterious far side of the moon.

"The soft landing and exploration of the far side, which has never been done before, will gain first-hand information about the terrain and lunar soil components and other scientific data, which will help enrich our understanding of the moon and the universe," said Zhang He, executive director of the Chang'e-4 probe project.

The scientific tasks of the Chang'e-4 mission include low-frequency radio astronomical observation, surveying the terrain and landforms, detecting the mineral composition and shallow lunar surface structure, and measuring the neutron radiation and neutral atoms to study the environment on the far side of the moon, the China National Space Administration (CNSA) announced.

China has promoted international cooperation in its lunar exploration programme, with four scientific payloads of the Chang'e-4 mission developed by scientists from Netherlands, Germany, Sweden and Saudi Arabia.

Three scientific and technological experiments, designed by Chinese universities, will also be carried out during the mission.

Scientists believe the special electromagnetic environment and geological features on the far side of the moon will be suitable for low-frequency radio astronomical observation and research into lunar substances composition.

However, landing and roving there requires a relay satellite to transmit signals.

China launched the relay satellite "Queqiao", meaning Magpie Bridge, on May 21 to set up the communication link between the earth and the moon's far side.

The satellite has successfully entered a halo orbit around the second Lagrangian (L2) point of the earth-moon system, about 455,000 km from the earth. It is the world's first communication satellite operating in that orbit, according to CNSA.

Named after Chinese moon goddess "Chang'e", China's lunar exploration programme, which began in 2004, includes orbiting and landing on the moon, and bringing samples back to earth.

The country's first lunar probe, Chang'e-1, was launched in 2007. Chang'e-2, launched in 2010, created a full lunar map with a resolution of 7 metres, as well as images of the Sinus Iridum, or the Bay of Rainbows, with a resolution of 1.5 metres, showing the details of the proposed landing site of Chang'e-3.

Chang'e-3, launched in 2013, was the first Chinese spacecraft to soft-land on and explore an extraterrestrial object. 

The scientific instruments on its lander are still operating, making Chang'e-3 the longest working man-made probe on the moon.

China launched an experimental spacecraft in 2014 to test technologies to be used on Chang'e-5, which is expected to bring moon samples back to earth.