Heidi Klum Looks on While Models Pose in Underwear on Flatbed Truck

Heidi Klum's not telling any of her potential top models to get a room ... 'cause she's cool with them rolling around in a bed outside -- for a photo shoot, that is!

The supermodel was rolling around Hollywood Thursday in a flatbed truck along with a full crew ... and, they all looked on while a photographer snapped pics of two half-naked models rolling around together on the mattress.

Watch the clip ... Heidi chats with the person next to her as the two subjects hit different poses in just their underwear -- flexing every muscle they've got for the cameras.

It's a pretty wild scene ... and, sources tell us it's all for the 20th season of "Germany's Next Topmodel."

We're told the production team is recreating challenges from the past ... including this one, where a couple of the model contestants are moving but still need to pose for photos.

Heidi posted a video from the set ... not clear what she's saying 'cause it's in German -- but, it looks like she's excited to be filming!

BTW ... Heidi's created viral moments like this while filming the show multiple times over the years -- including back in 2018 when she watched a model shower on a public street.