Boston officials gave their final approval to conversion of the Government Center garage complex into a $1.5-billion development containing high-rise offices, apartments, retail and a hotel.

Boston Redevelopment Authority directors on Thursday approved two towers for the first phase of development by National Real Estate Advisors and Boston-based HYM Investment Group.

A 480-foot-tall, 486-unit luxury apartment building designed by CBT Architects is set to break ground this spring along New Sudbury Street.  The project also includes a 43-story, 1-million-square-foot office tower designed by Pelli Clarke Pelli architects. Transwestern RBJ is representing the developers on the office project.

At full buildout, the project will include 812 residential units, 196 hotel rooms, 1.1 million square feet of office space and 85,000 square feet of new retail. Three smaller buildings containing a hotel and condos, boutique office space and multi-story retail will encircle a public plaza next to the Rose Fitzgerald Kennedy Greenway.

Once construction starts on the office tower, the portion of the garage that spans Congress Street and sections to the east will be demolished. Approximately 1,100 spaces will be retained.

“This project will reconnect four of Boston’s greatest neighborhoods – the North End, the West End, Beacon Hill and Downtown –  that have been divided by this hulking concrete structure for decades,” HYM Managing Director Thomas O’Brien said in a statement.

National Real Estate Advisors is a subsidiary of the National Electrical Benefit Fund, with $2.5 billion in assets under management.