Elon Musk said Thursday that he was helping combat falling birth rates after it was reported that he had twins last year with an executive at one of his companies.

"Doing my best to help the underpopulation crisis," tweeted the billionaire tech entrepreneur, who has fathered 10 children.

"A collapsing birth rate is the biggest danger civilization faces by far," Musk added.

He posted another tweet that read: "I hope you have big families and congrats to those who already do!"

The comments came a day after online outlet Insider reported that Musk had twins with 36-year-old Canadian Shivon Zilis, an executive at Neuralink, Musk's brain-implant maker.

She has also worked at other Musk companies including OpenAI and electric car manufacturer Tesla, Insider said.

In April, Zilis and Musk filed a petition with a Texas court for the children to "have their father's last name and contain their mother's last name as part of their middle name," Insider reported, referring to court documents obtained by the publication. 

The petition was granted in May, the site said. 

The babies, which Insider says were born in November, arrived just weeks before Musk, 51, and music artist Grimes had their second child via surrogate. 

They welcomed a baby girl named Exa Dark Sideræl Musk -- although the parents will mostly call her Y.

In total, the chief of Tesla and SpaceX has fathered 10 children, one of whom died shortly after birth.

In May, Musk tweeted a graphic from the Wall Street Journal showing that the average number of babies a US woman has in her lifetime fell from more than 3.5 in 1960 to a little over 1.5 in 2021.

He noted that it was below the 2.1 level that is needed for a generation to replace itself.

"USA birth rate has been below min sustainable levels for ~50 years," Musk wrote alongside.

Last month, one of his children who recently turned 18 filed a petition in a California court to change her name and gender identity to female.

She cited "the fact that I no longer live with or wish to be related to my biological father in any way, shape or form" as one of the reasons for the name change, according to the court document.