Fashion retailers have begun lining up as tenants at the massive Seaport Square development in South Boston, but the search for a supermarket and drug store continues.

Apparel, shoe and cosmetics stores will be a major part of the mix, said Brian Sciera, a vice president for W/S Development of Newton, a partner in the 6.5-million-square-foot project.

"The challenging thing is all of those players want to be on Seaport Boulevard because we’re creating a new market," Sciera said during an industry event Wednesday. "We’ve already started making some key fashion deals, none of which I can announce because they like to do that."

The mixed-use complex will contain 1.5 million square feet of stores and restaurants on the lower floors of buildings. The first phase consists of two buildings now under construction and two expected to break ground this year containing a total of 300,000 square feet of retail space.

Two buildings on Seaport Boulevard across from the federal courthouse that will contain 250,000 square feet of retail space are getting the most interest from retailers, Sciera said. Rents are still lower than Back Bay properties, Sciera said.

"Those fashion retailers want to see other traffic generators, too," Sciera said. "The one and one-A request from retailers and everyone we meet in the Seaport is: who is the pharmacy and who is the grocery store?’"

At full build-out, Seaport Square will contain 6.5 million square feet of retail, office, hotel and residential development.

Sciera spoke at a presentation by real estate executives near the site as part of a bus tour sponsored by NAIOP-Massachusetts.

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