I'm concerned for my neighbour

My two-doors-down neighbour has been having strange conversations with me lately about people recording him and conspiring against him. Things such as kids walking by his house recording video on their cell phones, trying to set him up on the bus, and even lightly accusing me of recording a bus stop across the road with my driveway camera. He's saying he has enough notes on people to "put them away" for a long time. This behaviour is new for him.

To make sure I wasn't off-base, I asked the neighbour between us if he thought this person was okay, to which he replied "I don't think so" and agreed there is reason to be concerned.

He lives on his own and we don't have contacts for any family member. I don't know what to do. Contacting the authorities for a wellness check would literally be this poor mans worst nightmare and potentially spiral him further.

Does anyone have suggestions on how to help?