Bruce Willis is thanking first responders in Los Angeles after wildfires took a toll on the city ... and he's making an extremely rare appearance in public.

The actor's wife, Emma Heming, just shared video of Bruce shaking hands and chatting up a couple LAPD officers on the streets of L.A.

Bruce is hardly ever seen in public these days in the wake of his dementia diagnosis. His wife and kids share photos of him every so often at family events, but we don't really see him outside anymore.

In the black and white video, Bruce is wearing a shirt, jacket and New York Yankees cap as he chats and shakes hands with a couple cops ... then snaps some photos with the officers.

Bruce's wife says ... "Spotting a first responder, Bruce never missed a chance to show his gratitude with a heartfelt handshake and a 'thank you for your service.' Yesterday was no different."

BW retired from acting in March 2022 when his family announced his grueling dementia battle.

It's pretty cool to see Bruce chopping it up with cops ... seeing as he plays an NYPD officer in "Die Hard."