State and local officials are rallying support behind a controversial zoning change that would permit the construction of a large-scale cold storage warehouse on Portland’s western waterfront.

The Portland Planning Board on Thursday will consider changes to a waterfront development zone west of the Casco Bay Bridge that would increase the maximum building height from 45 feet to 50 feet, and 75 feet under certain conditions.

Supporters insist the 68-foot-high building that cold-storage company Americold proposes is necessary to be financially viable and have the capacity to absorb growing traffic from Eimskip, the Icelandic shipping company that has made Portland its home port.

The zoning change would also allow other companies to develop in the zone, including nearby Portland Yacht Services, which is interested in building a maintenance building large enough to service ferries and other large boats.

“I believe it is good for the city, good for the state, good for the Port of Portland and certainly good for employing Portlanders,” said John Henshaw, director of the Maine Port Authority, which selected Americold to develop the state-owned parcel.

“A company is willing to invest its own money to help Portland grow that industry segment,” Henshaw said.

But the proposal has drawn fire from West End residents worried the building will block waterfront views, add traffic problems and lead to a wall of industrial buildings along West Commercial Street.

“This is the last mile of open waterfront. We don’t want to make into a truck hub, a shipping hub,” said Jo Coyne, a Salem Street resident.

Opponents of the zoning change are quick to say they are in favor of cold storage, but dispute the need for a building the size Americold proposes. Americold has a warehouse on Read Street, and some worry it will shift all its Portland operations to the new waterfront facility.

“Americold is holding a gun to the city’s head, saying, ‘We will have 75 feet or we’re out of here,’ ” Coyne said.

In January, the planning board appeared unconvinced of the need for the project and asked officials to justify the height increase.

In response, the Portland Economic Development Department produced reams of documents to prove its point. Those include an analysis from the engineering firm Woodard & Curran that concluded a 45-foot building would not meet Eimskip’s shipping needs past 2023 and keeping the building ceiling could increase the risk of losing the company as a shipping partner.

A traffic study concluded the project would not create traffic congestion or safety issues on West Commercial Street, while a draft market analysis said the project would have to be price-competitive with the Boston area, and that Americold’s proposal and a shorter alternative both fell within the size range built regionally and nationally.

Stephen Neel, a senior technical director with the Global Cold Chain Alliance trade group, said that building up, rather than out, is common in ports, where real estate is often constrained or very expensive.

“Does this one need to be 75 feet? I can’t speak to that,” Neel said. “All I can only say is that port facilities tend to operate at high volume and high turnover, and real estate historically is at a premium. That tends to create the need to build higher rather than broader.”

In a memo, the Portland planning office said the zoning change was a direct response to Americold’s request, but was like building heights allowed at other ports, including Bath, Portsmouth, New Hampshire, and New Bedford, Massachusetts, where structures between 70 and 100 feet are permitted.

As a trade-off for increased height, the proposed zoning change was amended so developments could only cover half of a lot, not the entire property, as is currently allowed. This would prevent the development of an “excessive street wall,” the planning office said.

While the debate has focused on cold storage, revising zoning would open the area to further maritime development, said Portland Waterfront Coordinator Bill Needelman, in a presentation to the Portland Area Chamber of Commerce last week.

“This process is about more than just cold storage. It is about modernizing land use opportunities for the entire port,” Needelman said.

“The regulatory framework has not generated significant development” since it was put in place in the early 1990s, Needelman said, adding that Portland has made more than 100 zoning changes in the last decade.

The reports generated to explain the need for the zoning change have not convinced opponents of the proposal. Tom Robinson, in a letter to the planning board on behalf of Portlanders for the Western Waterfront, said the Woodard & Curran analysis of Eimskip’s need was flawed and misleading.

“The city and the Port Authority have aggressively marketed these zoning changes by suggesting that without these changes development on the waterfront cannot move forward. We strongly disagree,” Robinson said.

“While we support cold storage, we strongly oppose turning the western waterfront into a truck hub that consolidates warehouse operations from other parts of the city,” he added.

Henshaw, from the port authority, acknowledges that Eimskip won’t be the only customer using the warehouse and some products will be trucked in and out.

“No developer is going to build cold storage for a single customer,” he said.

The opposition to the project is based on the mistaken idea that a 45-foot building could be built, he added.

“It is sort of meaningless to talk about a 45-foot building as an alternative when there is no proposal to build one,” he said.

The Waterfront Alliance, a group that seeks to advance the working waterfronts of Portland and South Portland, will hold an open house and discussion about the project Tuesday at the Mariner’s Church ballroom, 368 Fore St., Portland.

The program starts at 4 p.m. and a moderated discussion panel begins at 6:30 p.m.

Correction: This story was updated at 10:55 a.m. on May 16 to correct the spelling of Americold and Bill Needelman’s name.