Midtown's apartment market is about to get even busier.

Two Atlanta firms paid about $6.5 million for most of a city block in Midtown Atlanta and plan to develop a mixed-use project there that includes 321 luxury apartments and 8,600 square feet of retail space.

Bull Realty said the 2.5 acre site bordering Ponce de Leon Avenue, North Avenue, Piedmont Avenue and Juniper Street sold this month. The property features well-known architect I.M. Pei's first office building in Atlanta and the rest of the block, excluding St. Paul's Church.

The firm said the block was bought by a joint venture Sereo Group and Faison Enterprises Inc. Michael Bull, the firm's president, said there were 10 competing offers for the land.

It's one of a spate of new apartment projects in Midtown geared toward young and affluent residents.

Condo developer Jim Borders is backing a 23-story tower on Sixth Street and broke ground on another project, called SkyHouse Midtown, on 12th street. Further down 12th, Daniel Corp. and Selig Enterprises are building an $82 million glass apartment building with 330 units.