(Bloomberg News) Westfield Group, the world's biggest shopping center operator, has agreed to invest $612.5 million in a joint venture to develop the retail part of the World Trade Center.

The Sydney-based company has agreed in principle on a 50 percent share of a joint venture with the Port Authority of New York and New Jersey to develop the retail facilities on the lower Manhattan site, the company said in a statement to the Australian stock exchange.

Westfield became retail vendor for the area after acquiring an interest in July 2001, six weeks before the complex was destroyed in the Sept. 11 attacks, and sold it back to the Port Authority in December 2003. Westfield and the Port Authority started talks to develop the retail complex in January 2008 after signing a letter of intent. The current agreement will replace the initial letter of intent, Westfield said today.

The Port Authority and Westfield will jointly develop some 365,000 square feet of leasable retail space, and the shopping mall group will be in charge of management and leasing, it said. Another 90,000 square feet is expected to be added in the future, Westfield said.

Westfield shares fell 1.1 percent to A$7.96 at the 4:10 p.m. close of trade in Sydney, the lowest since May 25, 2009.

World Trade Center

The Port Authority owns the 16-acre (6 hectare) site, which also includes the 1,776-foot (541-meter) 1 World Trade Center, a 9/11 memorial and a mass-transit hub designed by Spanish architect Santiago Calatrava. The memorial plaza is slated to debut on the 10th anniversary of the attacks, and two skyscrapers, 1 and 4 World Trade Center, are to open in 2013.

A store-lined underground corridor will run from a new subway center at Fulton Street and Broadway, a block east of the trade center, to the World Financial Center on the Hudson riverfront, Chris Ward, executive director of the Port Authority, said on July 20.