An unmanned, privately-owned US space capsule which had delivered supplies to the International Space Station undocked from the orbiting outpost on Tuesday to start heading home, NASA said.

The manoeuvre with a robot arm handled by crew aboard the space station ended a mission of just over three weeks for the SpaceX company's Dragon capsule. At the point of disengagement, the capsule was high over southern Australia.

Dragon delivered 1,200 pounds (544 kilos) of food, scientific material and other supplies during SpaceX's second resupply mission to the ISS.

Once it is far enough away from the ISS, Dragon will fire up its orbital engines for about 10 minutes and is expected to drop into the Pacific with a parachute off the coast of Mexico at around 1636 GMT, NASA said.

The capsule is returning to Earth much heavier than on its outbound journey, as it will be carrying 2,668 pounds (1,210 kilos) of equipment from experiments conducted on the ISS.

One was designed to study molecular changes to a small flowering plant in microgravity. A related study examined how the plant roots hold up in low-oxygen environments.