NEW YORK (Reuters) - Mid-America Apartment Communities Inc (>> Mid-America Apartment Communities Inc) is close to finalising a $4 billion (£3.1 billion) deal to acquire Post Properties Inc (>> Post Properties Inc), a source familiar with the matter said on Sunday.

The acquisition is expected to be announced Monday and would create the largest publicly traded multifamily apartment real estate investment trust by number of units, said the source, who was not authorized to speak publicly about the matter.

For each share of Post Properties stock, shareholders would receive 0.71 share of newly issued MAA stock, the source said.

The deal, first reported by The Wall Street Journal, would combine companies buoyed by the rising demand for rental properties, creating an entity with more than 300 properties and 100,000 units, and a large presence in fast-growing metropolitan areas in Texas and Georgia, the source said.

MAA, based in Memphis, Tennessee, has a market value of $7.7 billion and owns all or part of 254 multifamily properties and 79,496 units in 15 states, according to its website and Thomson Reuters data.

Atlanta-based Post Proprieties, with a market value of $3.3 billion, has about 24,000 apartment units in more than 60 communities in Atlanta, Dallas, Washington, and Tampa, Florida, according to Thomson Reuters data.

(Reporting by Mike Stone; Writing by Alwyn Scott; Editing by Alan Crosby and Richard Chang)