A celebration at South Station as tower marches skyward

Two-plus years after the groundbreaking, officials gather to celebrate a complicated project that’s been decades in the making.

A ribbon-cutting ceremony was held at South Station, where the new 51-story mixed-use tower is under construction.John Tlumacki/Globe Staff

High above the train platforms at South Station on Tuesday morning, construction workers in hard hats and safety harnesses stood amid a dense network of steel support beams, aligning a hulking piece of steel like it was a puzzle piece.

Construction work on the 51-story, 678-foot tower above New England’s busiest train station, which started in January 2020, continued on Tuesday as civic leaders gathered to celebrate the project’s progress. Beyond the million-square-foot office and condo tower, the project’s first phase includes a new bus terminal and an expanded outdoor concourse.

A mixed-use real estate development at South Station has been in the works for decades. Houston development giant Hines closed on an air-rights agreement and financing on Christmas Eve in 2019, then started construction work the next month — just before the COVID-19 pandemic hit Boston.

At Tuesday’s event, Governor Charlie Baker cheered the investment into South Station — which he pegged at between $100 million and $150 million — and said the project was the type of project he looked forward to visiting “as a private citizen.” Baker also recalled the time he heard from his former transportation secretary that, after years of fits and starts, the project was moving forward.

The view down Atlantic Avenue from the site of a 51-story tower rising above South Station. John Tlumacki/Globe Staff

“I do remember the day when Stephanie Pollack reached out to our office and said, basically, ‘OMG, Hines has a financing partner,’” Baker said. “This thing had always been sort of banging around in the back of everybody’s mind as something that might actually happen. But there was always, frankly, a lot of doubt about whether or not anybody would be willing to take the chance that was associated with building this.”

David Perry, senior managing director at Hines, was smiling broadly on Tuesday. The level of coordination between private organizations and public agencies spanning the city, state, and federal governments to build a tower above a busy transit hub was considerable.

“We always felt it, over all these years, the support required from all levels of government, but to be here today, celebrating it together is really special,” Perry said. “It’s so gratifying, I can’t even begin to tell you.”

The project’s $1.5 billion first phase will include 166 luxury condominium units on its top floors, along with 670,000 square feet of office space. Hines had initially planned a hotel for the project’s next phase, but is reconsidering that, looking to possibly include life-science lab space or apartments instead. The second phase would start before work wraps on the office and condo tower in 2025, Perry said.

Mayor Michelle Wu and Governor Charlie Baker walked through the fifth floor of a new tower going up atop South Station on Tuesday.John Tlumacki/Globe Staff

The Hines team recognized that there are headwinds facing today’s office market, with demand for commercial office space less of a sure bet than it was pre-pandemic. No tenants have yet been signed. But, Perry said, South Station is “the best location in the city.” And including high-end condos in the mix for the 51-story tower is also a good economic bet.

“The future of demand for office space is less certain now than it was in 2019. I think that’s indisputable. That’s the sort of thing that creates uncertainty and causes concern,” Perry said. “We’re very pleased that we decided in this 51-story building, it’s not all office space. We kind of hedged our bets between residential and office, and thankfully the residential market is holding up really well.”

The celebration took place the day after the reopening of the MBTA Orange Line, which had not run for a month as the MBTA undertook five years’ worth of safety improvements. Boston Mayor Michelle Wu began her comments Tuesday by thanking the state state’s transportation secretary and the MBTA for “the hugely successful Orange line project done on time and with great results.”

“Just to show how much this region and city are committed to advancing this vision of transportation that undergirds of our economy, we’re here the very next day to celebrate a huge step forward,” Wu said. “This Transportation Center really will embody what we want people to feel about our city when they first set foot here and what the ethos of Boston is a place that is welcoming, connected and inspiring to all.”