A wealthy Melbourne family is putting up $4 million to build more than 50 portable homes for disadvantaged people on vacant VicRoads properties in a unique project to tackle the city's homelessness crisis.

The social housing project is mostly being privately funded by philanthropists Brad Harris, who co-owns the Sporting Globe Bar and Grill chain of nine restaurant-bars, and his father, Geoff Harris, who co-founded Flight Centre.

Brad Harris said homelessness was the No. 1 issue facing Victoria.

"Having a roof overhead and food in your stomach is fundamental. It's unacceptable that in a wealthy society like ours we've allowed this problem to grow worse," Mr Harris said.