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WASHINGTON — So many people are registering drones and applying for drone pilot licenses that federal aviation officials said Friday they are contemplating the possibility of millions of unmanned aircraft crowding the nation's skies in the not-too-distant future.

In the nine months since the Federal Aviation Administration created a drone registration system, more than 550,000 unmanned aircraft have been registered with the agency, said Earl Lawrence, director of the FAA's drone office.

Speaking at the first meeting of a new government-industry drone advisory committee, Lawrence said new registrations are coming in at a rate of 2,000 a day. By comparison, the FAA says there are 260,165 manned aircraft registered in the U.S.

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Related: FAA Chief: Drone Registration Soars Past That of Regular Planes

The FAA began issuing drone pilot licenses to commercial operators less than a month ago. Already, 13,710 people have applied to take the pilot exam, and 5,080 have passed it, Lawrence said. It's clear the agency's estimate of 15,000 licensed drone pilots by the end of 2016 will easily be exceeded, he said.

The FAA now forecasts there will be more than 1.3 million licensed drone pilots by 2020.

Lawrence asked the 35 committee members and dozens of attendees at the meeting: Will there eventually be hundreds of thousands of drones in the nation's skies? Or will there be millions?

Related: Drones for Businesses Can Take Off Under New FAA Regulations

Hobbyists and commercial operators alike are required by the FAA to register their aircraft, but agency officials acknowledged that they have no way of measuring how many unregistered drones are in use.

U.S. drone sales are expected to top 2.4 million aircraft this year, more than double last year's sales, according to the Consumer Technology Association, whose members include drone manufacturers.

NASA is working with industry and the FAA to create a new low-altitude air traffic control system specifically for drones. Industry and government officials say such a system will be needed if there are to eventually be widespread drone deliveries by Amazon and other companies. Google and the Chipotle Mexican restaurant chain are currently testing drone deliveries of burritos at Virginia Tech.