SAN FRANCISCO — SpaceX, the rocket maker founded by billionaire Elon Musk, has raised up to $350 million in new financing and is now valued at around $21 billion, making it one of the most valuable privately held companies in the world.

SpaceX’s new financing was disclosed in public filings that were obtained by Equidate, a marketplace for private company stock. SpaceX declined to comment.

With the latest funding round, SpaceX joins an elite club of seven venture-backed companies valued at $20 billion or more around the world, according to research firm CB Insights. Investors have poured money into the companies, many of which operate capital intensive businesses such as Uber and Airbnb, even as smaller start-ups have gone public and have seen their valuations waver.

Snap, the messaging and entertainment company, went public in March at a market capitalization of $24 billion, which has since fallen to about $16.5 billion. Meal delivery company Blue Apron went public last month at a market capitalization of $1.9 billion, which was less than its private market valuation; that has since dropped to around $1.3 billion.