There will be at least 2,000 fewer parking spots at LaGuardia Airport for about two years as it enters the next stage of a $4 billion redevelopment, the Port Authority said Wednesday.

The main parking garage, P2, in front of Terminal B will close Friday, eliminating at least 2,250 spaces, according to the authority, which operates the airport.

Also Friday, a new long-term parking lot, P10, with 1,800 spots, will open west of the airport at the Marine Air Terminal, and travelers will take a shuttle bus to the terminals, the agency said.

Three smaller lots and a smaller garage to the east of the main terminal will remain open for short-term parking during construction, the agency said.

The overall changes in eight lots and two garages means the airport will have 4,200 parking spaces as of Friday, down from 6,400 spaces in January, the authority said. That will not change significantly until early 2018, when a new garage with an estimated 3,000 spaces is expected to open near the main terminal, the agency said.

An aerial view shows LaGuardia Airport in Queens on June 20, 2016, before the beginning of a massive $4 billion renovation project, which will create terminals closer to the Grand Central Parkway. Photo Credit: FlyingDogPhotos.com / Kevin P. Coughlin

The parking figures provided by the Port Authority differed somewhat, sometimes by several hundred spaces, from those contained in agency planning documents, and those documents sometimes had conflicting numbers.

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An agency spokesman said Wednesday he could not explain the differences.

As the parking availability shrinks, the authority is encouraging people to take mass transit, and is touting a number of changes in bus routes to accommodate travelers.

“Redevelopment has begun, so consider other ways of getting to LGA” or LaGuardia, the Port Authority said in an advisory to motorists last week.

“Parking will be limited and some roads will be closed or detoured,” the agency said in another advisory. “Customers are urged to leave additional travel time and find other means of getting to the airport.”

The Metropolitan Transportation Authority mounted a publicity campaign last month to tout the benefits of using the Q70 bus, running between the airport, and subway and Long Island Rail Road connections in Woodside and Jackson Heights.

Buses on the Q70 will be “rebranded” in September, the MTA said, by painting them teal and dotting the exteriors with silhouettes of airplanes and clouds. Travelers using their MetroCards on the subway from Manhattan to stops in Queens can transfer for free to the Q70.

The Port Authority said it has been working with the airlines and others to inform passengers about the parking situation.

“The outreach includes: radio ads, airport networks video messaging, web advertisements, on-airport banners, text and email e-alerts, social media, news releases and media interviews,” the authority said in an email statement.

It said airport users can go to its website — laguardiaairport.com — to reserve parking and see the percentage of available slots in parking areas.

The parking-lot shuffle comes as a private consortium, LaGuardia Gateway Partners, begins building a new main terminal while keeping the existing one open for business.

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The existing Terminal B is used by eight airlines, including American, JetBlue and United. Negotiations are continuing for the redevelopment of Terminal C to the east, home to Delta Air Lines.

The new Terminal B and related work will cost about $4 billion and be funded through public and private funds. The terminal will be built and operated by the consortium under a lease that runs through 2050.