WASHINGTON (CNN) -- A private plane entered the restricted airspace over Washington on Wednesday, prompting some people to evacuate buildings on Capitol Hill but posing no imminent threat, officials said.
A short time later, Capitol Hill police gave the all-clear and said the aircraft landed outside the restricted zone.
There was no evacuation of the U.S. Capitol building and "things are back to normal," police said.
The North American Aerospace Defense Command said the plane, a small Cessna, landed at a regional airport in Leesburg, Virginia, where the pilot waited for authorities to arrive.
The U.S. Coast Guard, which monitors the airspace above the district, scrambled helicopters as a precaution, an official said. The U.S. military also dispatched F16s out of Andrews Air Force Base as a precautionary measure, NORAD said.
Such airspace violations are not uncommon.
Speaking at a House Energy subcommittee hearing, Rep. Bart Stupak notified the committee participants that an alert had been issued.
"We have an air code yellow, meaning a plane is in our airspace," he said at around 12:25 p.m.
He said he was on stand-by for a possible evacuation order, but it was never issued and the hearing, to address the safety of the nation's meat supply, continued uninterrupted.
People were seen crowding the streets near the Capitol after word spread of the aircraft's incursion.
There are two concentric restricted zones over the District of Columbia, the outermost called the Air Defense Identification Zone.
Many pilots unintentionally violate the ADIZ as they move out of the zone's outer fringes.
The ADIZ was reshaped on August 30, 2007, from a "Mickey Mouse" shape to a circular shape to help reduce accidental incursions.
The innermost restricted airspace is the Flight Restricted Zone, or FRZ -- a smaller and more restrictive zone. With a few exceptions, only scheduled airlines and governmental flights are allowed in the FRZ.
The Federal Aviation Administration added four air traffic controller positions last summer to help pilots transit the airspace. Pilots had complained about having trouble getting permission to enter the airspace, forcing them to circle outside, which sometimes caused safety issues.
The ADIZ has been the bane of general aviation pilots in the region, according to some experts. Some 20,000 people commented on an FAA proposal to make the ADIZ permanent, and some pilots fear the government will seek to expand the restrictions to other cities. E-mail to a friend
CNN's Jeanne Meserve, Mike Ahlers, and Mike Mount contributed to this report