Construction got officially underway Jan. 24 on Bulfinch Crossing, the 2.9 million-square-foot, six-building redevelopment of much of downtown Boston’s Government Center Garage.

Work on the project, which is one of the biggest developments in the Boston region, has actually been ongoing for months; but the development team of National Real Estate Advisers and the HYM Investment Group wanted to make it official nonetheless.

Construction is supposed to wrap by September 2019.

When completed, Bulfinch Crossing is expected to include 812 residential units; 196 hotel rooms; 1.15 million square feet of office space; and 85,000 square feet of retail. It will also include around 1,100 parking spaces for residents and the public; and a one-acre "rooftop amenity," according to a release from the developers.

The first building to go up will be a 45-story, 486-unit apartment building on New Sudbury Street. A 43-story, 1 million-square-foot office building called One Congress will go up next on New Chardon Street as will a 28-story building on Congress Street with either apartments or condos (the market will likely decide).

CBT Architects and Pelli Clarke Pelli are designing the complex. Bulfinch Crossing will be 528 feet at its highest point.

And, to give some perspective of the scope, 200 Clarendon (a.k.a. the Hancock) is about 2 million square feet and the Pru is about 1.2 million. Below are renderings of the project, courtesy of HYM Investment.