A European rocket blasted off Wednesday bearing a 20-tonne supply ship destined for a rendezvous with the manned International Space Station.

The super-charged Ariane 5 ES rocket departed from Kourou, French Guiana, just shy of 2151 GMT after an initial attempt the day before was scratched at the last minute due to a minor technical glitch with the fueling system.

The liftoff had to take place at that time and no other.

"As we are going to the ISS so we have to leave the ground at a specific instant, so there is no launch window," explained Arianespace Chairman Jean-Yves Le Gall minutes before the launch.

The first phase of the mission was declared a success after the rocket's last stage fell away from the European Space Agency (ESA) supply vessel exactly 64 minutes into the flight, somewhere over the Tasmanian Sea.

"Europe has again been extremely successful with the perfect orbiting of the ATV Johannes Kepler. This launch was exceptional," Le Gall said to rousing applause at the control centre in Kourou.

Named for the great 16th and 17th century German astronomer, the Johannes Kepler is the second Automated Transfer Vehicle (ATV) that Arianespace will have delivered to the ISS. The first was hoisted into space in March 2008.

Weighing in at more than 20 tonnes, it is by far the heaviest payload ever hoisted into orbit by an Ariane rocket, nearly 15 times heavier than the pencil-thin trailblazer catapulted into space in 1979.

The automated vehicle is slated to supply the ISS with life-sustaining air, food and spare parts, and to reposition the sprawling station -- which, tugged by Earth's atmosphere, has lost altitude -- into its optimal orbit.

It is currently around 360 kilometres (225 miles) above Earth and needs boosting to some 400 kilometres (250 miles).

"Ariane has completed its mission. Now ATV is starting its mission," said Jean-Jacques Dordain, ESA's Director General.

Once separated from the launch vehicle the ATV is autonomous, using its own systems for energy and guidance in liaison with a control centre in Toulouse, southwestern France.

Within 30 minutes, it will have deployed four large solar panels which, along with onboard batteries, power the vehicle.

The unmanned supply ship is scheduled to dock with the ISS on February 24, a feat of precision unmatched by any other space power.

"We will be working at a speed of around 28,000 kilometers (17,500 miles) per hour and our approach will be at seven centimetres (2.8 inches) a second, so although we are moving at this high speed, we will really be approaching the ISS very gently," said mission director Kris Capelle ahead of the launch.

Once emptied of its cargo, the supply ship -- a cylinder 10 metres (33 feet) long and 4.5 metres (15 feet) in diameter -- will then be used as a spare room and for storage, easing the cramped conditions for the ISS crew.

In early June the ATV will undock, laden with rubbish, human waste and unwanted hardware, and then go on a suicide plunge, burning up over the South Pacific.

ESA is scheduled to build five automated supply ships for the ISS.

Each successful mission boosts the case for scientists who want the ATV to be the template of a manned spacecraft, placing ESA on an equal footing with the United States, Russia and China.

"This is also the success of Astrium and the European space industry. They have joined the club of the major players," Le Gall said.

Astrium has led a consortium of European manufacturers in building the ATV, composed of a service module with avionics and propulsion systems, and a pressurised cargo carrier.

Today's launch will be the 200th for Arianespace, which has lifted nearly 400 commercial and military satellites into space.