NASA's Kepler space telescope has discovered 1,284 new worlds, 100 of which are similar in size to Earth and nine of which could potentially harbour life, according to the United States space agency.

It is the largest single finding of new planets ever and more than doubles the number that Kepler has found to date.

"This gives us hope that somewhere out there, around a star much like ours, we can eventually discover another Earth," said Ellen Stofan, NASA chief scientist in a statement.

The discovery follows an analysis carried out on the catalogue of 4,302 potential planets found by Kepler by July of last year.

1,327 were ruled out as they did not reach the 99% probability threshold required for them to be deemed a candidate planet.

707 were considered by scientists more than likely to be some other form of astrophysical phenomena, while 984 had previously been verified to be planets by other means.

That leaves 1,284 other worlds where the probability of being a verifiable planet stands at over 99%.

550 could be rocky planets like ours, NASA says, with nine in the habitable zone - a position not too close or too far from the star that they orbit, which means water and therefore life could potentially exist on them.

The addition of the nine means there are now 21 known exoplanets in this so-called "Goldilocks Zone".

The researchers used a statistical analysis method which can be used on many candidate planets at the same time - speeding up the verification process considerably.

Previously astronomers had to process and verify each potential planet one by one.

The method Kepler uses to detect potential planets has a resonance with yesterday's transit of the Sun by Mercury.

The telescope looks for reductions in the brightness that happens when planets pass in front of their stars.

Full details of the discovery are contained in a paper published in the Astrophysical Journal.