Gov. Andrew M. Cuomo unveiled a proposal Thursday to upgrade the Jacob K. Javits Convention Center “for the next generation,” expanding space in the facility on Manhattan’s far west side by more than half with a $1 billion face-lift.

The plan also would create new underground garage space and enhance green-energy capabilities, Cuomo said at a news conference at the 30-year-old complex.

The Javits Center is the “busiest convention center in the country,” but it needs to be modernized to compete with other sites nationwide, the Democratic governor said.

Under his plan, construction will begin later this year to build 1.2 million additional square feet. The expansion will add new space outward — on the north end of the complex — and upward, but none would be higher than the existing roof, said Dani Lever, a Cuomo spokeswoman.

The revitalization will be financed within the center’s existing budget and through the Empire State Development Corp., Lever said. No further approvals are needed, she said.

“This will be a convention center for the next generation,” Cuomo said, adding, “It fits in with the vision of building New York to lead.”

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The complex will stay within its six-block-long footprint, but grow to 3.3 million square feet under Cuomo’s plan.

Past efforts to expand the city’s convention space foundered.

In 2012, the governor pitched — but failed to deliver — what he envisioned would be the nation’s largest convention center at the Aqueduct Racetrack in Queens. Former Gov. George Pataki and ex-Mayor Michael Bloomberg in 2004 announced plans to dramatically remake Javits and build a Jets football stadium on the west side, but that project was defeated.

Cuomo said Thursday that new Javits proposal — the latest in a line of infrastructure upgrades he is championing including makeovers of LaGuardia Airport and Penn Station — is not just a vision. “It’s going to happen,” he said.

The facility is home to annual events such as New York Comic Con and the New York Boat Show. The upgrade will add $393 million in annual economic activity from conventions, trade shows and other events and 4,000 full-time jobs, Cuomo said.

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It will have 1 million square feet of total event space, five times more meeting room space and the “largest ballroom in the Northeast,” the governor said. It will use more solar power and include an on-site garage to reduce noise and carbon pollution, he said.

Groups including the Building and Construction Trades Council of Greater New York and the Hotel Association of New York City on Thursday welcomed the plan.

Delores Rubin, chair of the local community board, said she was hopeful that Javits officials and her group “will be on the same page.”

With Ivan Pereira