Although work on the massive Downtown East development has been underway since the beginning of April, construction officially kicked off Tuesday morning at a groundbreaking ceremony in downtown Minneapolis.

Local developer Ryan Cos., which spearheaded the $400 million project, organized the event.

“This is historic,” Ryan Cos. CEO Pat Ryan said. “I think this will be considered one of the most transformational public-private partnerships in the country.”

The development — consisting primarily of two 18-story residential and commercial towers, a nearly two-block public park and a 1,610-stall parking ramp — will be built on five blocks of downtown real estate that Ryan Cos. and the Minnesota Sports Facilities Authority purchased from the Star Tribune newspaper.

Ryan said the complex project’s success required several pieces to come together — including the selection of an adjacent site for the new Vikings stadium and San Francisco-based Wells Fargo’s commitment to buy much of the office space in the towers.

“It didn’t happen easy,” said former Minneapolis Mayor R.T. Rybak, one of the development’s most visible and vocal advocates.

Collin Barr, president of Ryan Cos. operations in the northwest region, said its complexity and 18-month turnaround time meant the project “was by no means a slam dunk.”

Rybak and current Mayor Betsy Hodges both expressed confidence that the project would spur future development in the city’s downtown.

Across the street from the groundbreaking ceremony, crews already were excavating the base of the first tower, which is expected to be completed in late 2015; the second is to be completed about eight weeks later. Wells Fargo plans to move into its new office space during the first quarter of 2016.

Construction of the parking ramp is expected to begin later this year and is expected to wrap up toward the end of 2015.

The public park is expected to be completed in time for the 2016 football season.

Nick Woltman can be reached at 651-228-5189. Follow him on Twitter at @nickwoltman.