Nasa's most powerful rocket yet is set to blast off on Monday night Hong Kong time for the maiden voyage of a mission to take humans back to the Moon, and eventually to Mars.

Fifty years after the last Apollo mission, the space programme called Artemis is to get under way with the blast off of the uncrewed 98-metre Space Launch System (SLS) rocket at 8.33p Hong Kong time from the Kennedy Space Center in Florida.

Tens of thousands of people are on hand along the beaches of Florida to watch this launch that's been decades in the making. They include Vice President Kamala Harris.

Hotels around Cape Canaveral are booked solid with between 100,000 and 200,000 spectators expected to attend the launch.

The goal of the flight, baptised Artemis 1, is to test the SLS and the Orion crew capsule that sits atop the rocket. The capsule will orbit the Moon to see if the vessel is safe for people in the near future. At some point Artemis will see a woman and a person of colour walk on the Moon for the first time.

"This mission goes with a lot of hopes and dreams of a lot of people. And we now are the Artemis generation," Nasa administrator Bill Nelson said on Saturday.

The massive orange-and-white rocket has been sitting on the space centre's Launch Complex 39B for a week. Its fuel tanks were to be filled overnight on Sunday into Monday with more than three million litres of liquid hydrogen and oxygen.

Nasa said there is an 80 percent chance of acceptable weather for a liftoff on time at the beginning of a launch window lasting two hours.

For the first time a woman – Charlie Blackwell-Thompson – will give the final green light for liftoff. Women now account for 30 percent of the staff in the control room; there was just one back with Apollo 11.

Cameras will capture every moment of the 42-day trip and include a selfie of the spacecraft with the Moon and Earth in the background.

The Orion capsule will orbit around the Moon, coming within 100km at its closest approach and then firing its engines to get to a distance 64,374km beyond, a record for a spacecraft rated to carry humans. (AFP)