The South Africa-born billionaire's space company has found massive success as a NASA contractor, but critics have for years panned Musk's Mars colonization plans as overambitious.

The move also puts Musk in alignment with US President Donald Trump's shift away from sending Americans to Mars.

"For those unaware, SpaceX has already shifted focus to building a self-growing city on the Moon, as we can potentially achieve that in less than 10 years, whereas Mars would take 20+ years," Musk said in a post on X, the social media platform he bought in 2022.

Difficulties in reaching Mars include the fact that "it is only possible to travel to Mars when the planets align every 26 months."

"We can launch to the Moon every 10 days," he added.

Musk has blown through several previous estimates on when he could feasibly put man on the Red Planet.

In 2016, Musk said passengers could take off for Mars as soon as 2024, if financing and other planning factors for his rockets came through.

That prediction came after he told the Wall Street Journal in 2011 that SpaceX astronauts would reach Mars in "Best case, 10 years, worst case, 15 to 20 years."

In an executive order on US space policy late last year, Trump said he wanted to get Americans to the Moon by 2028, under NASA's Artemis program, for which SpaceX is a contractor.

That marked a shift from Trump's earlier declaration that he wanted to plant the American flag on Mars before the end of his four-year term.

Americans are currently scheduled to return to the Moon's surface in mid-2027 on the Artemis 3 mission, but the timeline has been repeatedly pushed back.

Industry experts say it will probably be delayed again because the lunar lander in development at SpaceX is not ready.

Easier access to the Moon "means we can iterate much faster to complete a Moon city than a Mars city," Musk said Sunday.

But he added that SpaceX would not give up on its Mars plans, saying it would "also strive to build a Mars city and begin doing so in about 5 to 7 years."