A nearly 400-foot tower that would transform Portland’s skyline moved one step closer to reality Tuesday night when it received unanimous approval from the city’s Planning Board.

The 30-story mixed-use, high-rise building is proposed for 45 Union St., adjacent to the Old Port.

Now, the developer will need to secure building permits, finalize financing and begin work on detailed construction documents. The project does not require any approval from the City Council.

The tower, proposed by Portland developer East Brown Cow Management LLC, would stand at 380 feet, making it far and away the state and city’s tallest building. It would include more than 70 residential units, commercial space, an 88-room hotel and a restaurant at the top, and is just one part of a project called Old Port Square, designed to fill an entire city block.

Portland updated its zoning laws last year with the goal of allowing growth in the city while preserving its character. The overhaul included an increased maximum height for buildings in some of the city’s major corridors, permitting buildings up to 380 feet in downtown.

On Tuesday night, the board heard presentations about traffic impacts of the proposal and reviewed the developer’s latest revisions to the application before receiving a final round of public comment.

That testimony, both in person at the meeting and in submitted written comments, was mixed.

Local organizations, including Greater Portland Landmarks and the Portland Regional Chamber of Commerce, expressed support for the project, describing it as a modern but thoughtful design that would transform an underutilized parking lot into a vibrant mixed-use space.

“This project shows that Portland can honor its history while preparing for its future,” said Thomas O’Boyle, director of advocacy at the chamber.

But other residents and local business owners criticized the building as an eyesore, whose height would disrupt Portland’s skyline and conflict with the city and Old Port’s historic character. Several commenters said the city, in need of more affordable housing, should prioritize those projects over new high-end apartments and a hotel.

In accordance with Portland’s inclusionary zoning rules, developers are planning to pay about $3.3 million into the city’s Jill C. Duson Housing Trust Fund in lieu of building affordable housing units.

During deliberations, the board acknowledged public concerns about the skyline and how it might visually transform the city, but noted that the applicants had met board standards. Members acknowledged that after raising the city’s maximum permitted downtown building heights last year, someone had to be the first to build in the new allowable space.

The planning board approved the project unanimously, although several members were absent.

The board also passed language requiring that if the developer makes major material or architectural changes that substantially differ from the approved plans, they must submit those changes to the board for review.