China's lunar probe, the Chang’e 3, is expected to reach a circular orbit about 100 kilometres above the moon tonight, the Beijing Morning Post reports.
The probe will stay there for about a week, making observations and testing equipment before touching down on the lunar surface and releasing a robotic rover next weekend.
The moon arrival was earlier than scheduled because Chinese space authorities cancelled a routine orbital manoeuvre, according to Xinhua.
They planned to fire the probe's rockets three times to bring it on to the transitional orbit of the moon but the third was no longer necessary after the first two manoeuvres hit their target, authorities said.
The major challenge will be the soft landing.
It is the first time that China has used a rocket engine that can vary its thrust in a space mission.
3D Animation: hello from the Moon