Hines would build the tower above the rail shed at South Station, with a lobby along Atlantic Avenue. That lobby would fill in the gap between South Station’s main concourse and its bus terminal, and would expand the bus facilities by 50 percent. It would also expand a parking garage, adding 527 spaces.

The Boston Planning & Development Agency board approved plans for a 51-story office and condominium tower over the busy rail hub. Development firm Hines hopes to break ground in April, though it’s still negotiating final details of the plan with state transportation officials.

An ambitious but long-stalled plan for a skyscraper atop South Station won a key city approval Thursday night. But it will need to clear significant hurdles from the property owner -- the state transportation agency.


Above that, Hines would build 1.1 million square feet of office space and condos in what, at 677 feet high, would rank among the city’s tallest buildings. Later phases would add two mid-rise buildings atop the station.

The complex project has been on the drawing boards for a quarter-century, and Hines won approval from the city for a different version of the project in 2006. It sat dormant until the Houston-based developer revived it this summer with tweaked plans and investment from a large Chinese homebuilder.

There is a sense of urgency. Under its development deal with MassDOT, Hines must come to terms with the state and start construction by April 30. David Perry, who heads the firm’s Boston office, said he was confident the company will make that deadline.

Hines would begin building even if it doesn’t have an anchor tenant lined up for the office space. Because of its location above a busy rail hub, the project will take four years to build, Perry said, and tenants are not likely to sign a lease that far in advance.


Building on spec, as it’s called, is unusual for a major office development in Boston, but Perry said he believes it will fill up.

“The location is unsurpassed,” he said. “There’s been a lot of interest.”

A MassDOT spokeswoman said the agency is actively negotiating with Hines over changes to the station, street access, parking, and other details.

Also Thursday, The BPDA approved a new zoning plan in South Boston that will dramatically increase density along Dorchester Avenue, paving the way for 6,000 to 8,000 new housing units there over the next decade. It’s the first of several transit-oriented rezonings launched by the Walsh Administration to win BPDA approval.

And the board approved a $110 million, 13-story office building in the Raymond L. Flynn Industrial Park on the edge of the Seaport; the $71 million rehabilitation of an affordable senior apartment building in Chinatown; and mid-size apartment buildings in Roxbury and Jamaica Plain.

Tim Logan can be reached at tim.logan@globe.com. Follow him on Twitter at @bytimlogan.