Developers who are renovating the Nassau Coliseum have removed the arena’s old seats, gutted the entranceway and removed extensive amounts of asbestos, but say it will take until March 2017 to reopen the arena, three months later than originally planned.

Brooklyn developer Bruce Ratner, who is spending $260.5 million to renovate the arena and build an adjacent retail and entertainment complex, made the disclosures Wednesday during a news media tour of the Coliseum construction project.

While the Coliseum’s exterior is largely unchanged, construction inside is progressing rapidly, Ratner said.

“We promised you beautiful architecture and an iconic building,” he said. “You will find when this is completed that it will be one of the great structures in this country.”

Ratner, executive chairman of Forest City Ratner Cos., said delays in starting construction last year pushed back the opening date. Ratner said he had expected to begin work in August, but construction was delayed because of a dispute over the use of union labor to build the interior of the retail complex. Work began in November.

A Dec. 10, 2016, game between the University of Kentucky men’s basketball team and Hofstra University, originally to be played at the Coliseum, will be played at Barclays Center in Brooklyn, a Ratner spokesman said.

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To date, 1,000 tons of debris have been removed from the Coliseum, an unspecified amount of asbestos has been removed and the concourse has been stripped of virtually all remnants of the old arena, including the New York Islanders’ logos and colors. Forest City Vice President Rebecca D’Eloia said the company was considering ways to memorialize the building’s history, including the Islanders’ 43-year tenure at the arena, on a wall on the Coliseum’s lower level.

Subject to National Hockey League, the Islanders are scheduled to play four regular season and two preseason games, and to hold practice and autograph sessions at the renovated arena, Nassau County Executive Edward Mangano said.

Mangano said Wednesday that the six Islanders games would “provide an outlet for our Long Island fans to view their favorite team right here. . . . And who knows what the future holds?”

But NHL Commissioner Gary Bettman said the Igames are not a done deal.

“There are a whole series of factors that would have to go into whether or not that’s even feasible, and since there’s not even a formal request I’m not even going to speculate what those factors are,” Bettman said.“ If anyone is suggesting it’s a done deal, they’re not aware of all of the factors involved,” he said.

Ratner said Wednesday that he was “committed” to bringing an American Hockey League minor league hockey team to the Coliseum, but offered no further details.

Last week, the Association for a Better Long Island, a Hauppauge-based development group, urged Mangano to rescind Ratner’s lease to redevelop the Coliseum, citing “a noticeable lack of activity” at the arena. The group also said there should have been hearings after Ratner sold an 85 percent share of the Coliseum redevelopment company to Brooklyn Nets owner Mikhail Prokhorov.

ABLI President Lorraine Harris said Wednesday that the group’s position was unchanged. “We remain concerned about the pace of construction and believe the level of information provided to date is less than the public deserves,” Harris said.

Edward Blumenfeld, president of Syosset-based Blumenfeld Development Group, who sits on the board of the ABLI, filed suit against Ratner after he was ousted from his lead role in developing the retail complex.

Officials provided new details about the timing of the renovations and some of the interior improvements.

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The exterior facade of the Coliseum will be replaced in late summer or early fall, and new seating will be installed near the end of the year, said Forest City executive Vice President James Lester.

The developers will install new mechanical, plumbing and electrical systems, double the bathroom capacity, add new tiling and expand the concourse in the coming months, said Peter Wang, a design director with Gensler, a Manhattan-based architectural firm.

Similar to the Barclays Center, visitors at the front entrance will have a direct view of the Coliseum’s bowl, while a new lighting system will decorate the arena’s ceiling for concerts.

“When all is said and done, Long Island will have a shiny new venue; a top of class entertainment and sports venue,” said Wang, who is not related to Islanders owner Charles Wang.

The renovated arena will be downsized from more than 17,000 seats to 13,000 seats for hockey, 13,500 for basketball and 14,500 for most concerts.

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With Jim Baumbach