(Web Desk) - The man behind SpaceX, Elon Musk, has pledged to take humans to Mars in just four years time onboard his Starship mega-rocket.

The eccentric billionaire, who also owns Tesla and X, said Starship's first flight to Mars will occur in two years time, when the next Earth-Mars transfer window opens.

Earth-Mars transfer launch windows occur every 26 months.

"These will be uncrewed to test the reliability of landing intact on Mars," Musk wrote in a post on X, announcing the new target timelines.

"If those landings go well, then the first crewed flights to Mars will be in 4 years."

Musk doesn't just have hopes of taking Earthlings to the Red Planet, but of building a Martian metropolis there, too.

"Flight rate will grow exponentially from there, with the goal of building a self-sustaining city in about 20 years," he added in the same post.

"Being multiplanetary will vastly increase the probable lifespan of consciousness, as we will no longer have all our eggs, literally and metabolically, on one planet."

Starship, at nearly 400ft tall, with 33 engines, is the tallest rocket ever leave the ground.

It was designed from the onset to be able to carry more than 100 tons of cargo to Mars and the Moon, so it can store everything needed to build off-planet base camps.

Not only is it the tallest rocket to ever be flown, the first stage of Starship, known as the Super Heavy booster, is the most powerful rocket ever built and can produce up to 7.6million kilograms of thrust.

That is nearly double the current record held by Nasa’s Space Launch System (SLS).

Starship is being developed as part of a $1.15billion contract with Nasa to deliver astronauts to the Moon in the US space agency's Artemis programme.