Elon Musk is has declared "all systems green" for the test flight of the most powerful rocket ever built, Starship, designed to one day send astronauts to the Moon and Mars.

The 390ft rocket, which has been picked by NASA for its return to the lunar surface, is on the launch pad at the billionaire's SpaceX spaceport in Boca Chica, Texas. It is due to launch at any moment from 2.28pm UK time.

The mission has already been delayed once, after a frozen valve led to issues with fuelling the rocket during its first attempt on Monday.

Mr Musk has sought to manage expectations for the first launch, saying on Sunday his main objective for the mission was "just don't blow up the launchpad."

The super heavy Starship rocket has been picked by the US space agency for its 2025 Artemis III Moon mission, the first time mankind will return to the Moon's surface since the Apollo programme ended in 1972.