If the governing body of each of 2 or more communities declares, by resolution, that there is a need for 1 slum clearance and redevelopment authority to be created for all of such communities, and has made the findings required by § 4504 of this title, a public body, corporate and politic, to be known as a regional slum clearance and redevelopment authority (herein referred to as regional authority or authority) shall thereupon exist for all of such communities and may exercise the powers and other functions of an authority under this chapter in such communities.