Nasa launched the most powerful rocket ever built on a journey to the Moon on Wednesday, in a spectacular blaze of light and sound that marked the start of the space agency's new flagship program, Artemis.

The 32-story tall Space Launch System (SLS) blasted off from the storied Kennedy Space Centre in Florida at 0647 GMT.

"We are going," tweeted the space agency.

Fixed to its top was the uncrewed Orion spaceship that will later separate and complete an orbit-and-a-half of Earth's nearest neighbor, in a test run for later flights that should see the first woman and first person of color touch down on lunar soil by the mid-2020s.

America last sent astronauts to the Moon during the Apollo era, from 1969-1972. This time it hopes to build a sustained presence – including a lunar space station – to help prepare for an eventual mission to Mars.

The launch came despite technical issues that ate into the two-hour launch window.

Engineers were forced to pause the flow of liquid hydrogen into the core stage on Tuesday night because of a valve leak, though a team sent to the launch pad resolved the problem after an hour.

Later, the space agency reported that a radar site monitoring the rocket's flight path was experiencing problems due to a faulty ethernet switch that had to be replaced.

It was third time lucky for Nasa after two previous launch attempts were cancelled for technical reasons. Launch was also delayed due to weather setbacks, including Hurricane Ian that battered Florida in late September.

The Orion crew capsule was being lifted by two boosters and four powerful engines under the core stage, which detached after only a few minutes.

After a final push from the upper stage, the capsule will be well on its way, taking several days to reach its destination.

Rather than landing on the Moon, it will assume a distant orbit, venturing 64,000 km beyond the far side – further than any other habitable spacecraft so far.

Finally, Orion will embark on the return leg of its journey. When passing through the atmosphere, the capsule's heat shield will need to withstand a temperature half as hot as the Sun's surface.

The mission will last 25 and a half days, with a splashdown in the Pacific Ocean on December 11. (AFP)