Sergey Brin, the Google co-founder, has reportedly been building an airship inside of Hangar 2 at the NASA Ames Research Center, Bloomberg reports.

The airship apparently looks like a classic zeppelin and it is housed at NASA's Ames research facility, the publication's sources say, but it's not clear whether the airship a prototype for a business venture, or just a passion project for the billionaire.

Alan Weston, the former director of programs at NASA Ames, is leading Brin's airship project, according to the report.

Weston didn't respond to Bloomberg's request for comment, while Brin himself said he "[didn't] have anything to say about this topic right now."

Brin's airship is separate from a freight project called Calcifer that was shelved by Google X, the company's experimental research lab, in 2014.

Alphabet CEO Page, Brin's Google co-founder, has funded at least two secretive flying-car projects - startups Kitty Hawk and Zee.Aero, also separate from Alphabet. On Monday, Kitty Hawk released a video showing one of its all-electric vehicles taking off and soaring over a lake with the driver perched on top.