The Federal Aviation Administration notified pilots over the weekend of a sighting of a large white balloon roughly 600 miles east of Hawaii at an altitude of 40,000 to 50,000 feet.

The apparent sighting comes amid a surge in interest in unidentified flying objects after the U.S. military shot several objects out of the sky this month, including one that it maintains was a Chinese spy balloon and several other objects the White House says may have been balloons used for commercial or scientific activity.

Messages from the Aircraft Communications, Addressing and Reporting System — or ACARS — showed aircraft acknowledging the alert, which had included a request to pilots report back if they spotted any such object.

When asked for comment on the balloon’s current whereabouts and what sort of balloon it was believed to be, the FAA responded with an email that said only “we will keep you posted if we have anything to share.”

A military spokesperson said the U.S. Indo-Pacific Command “is aware of the reports of a large white balloon by civilian aircraft” and that “we are looking into the reports and have nothing additional at this time.”

The Warzone Wire blog, which provides military and defense news and analysis, reported that on Sunday a Navy P-8 Poseidon surveillance plane flew from Hawaii to the general area where the balloon had been reported for about six hours before returning, though it’s not clear the flight was related to the balloon sighting.

High-altitude balloons are not uncommon and can be used for a variety of commercial and scientific purposes, as well as by hobbyists. Last March, Honolulu residents spotted two balloons over the city that turned out to be a product test by Aerostar, which has used balloons to monitor wildfires and provide mobile network coverage after natural disasters. The company’s clients have included Google, NASA and the U.S. Air Force.

Aerostar’s balloons were equipped with transponders that allowed the FAA to identify them and monitor their location. Anything flying without a transponder potentially causes a risk of collision with aircraft, a concern in Hawaii’s busy skies.

In February 2022, Hawaii National Guard F-22 fighter jets scrambled in response to what the military referred to as an “unmanned balloon without observable identification markings” lingering off Kauai and watched by island residents. Military officials acknowledged “actively monitoring” the balloon for weeks but declined to provide additional details.

This month, Pentagon spokesperson Brig. Gen. Pat Ryder said the Chinese government has been using balloons for several years as part of a surveillance program that has sent balloons into U.S.-controlled air space on at least four occasions, but declined to confirm whether the Kauai incident was one of them, saying only that balloons flew near “sites that would be of interest to the Chinese.”

Kauai is the site of the Navy’s Pacific Missile Range Facility, a key weapons- testing facility that has also been regularly watched by Russian surveillance ships, most recently in January.

Several media reports suggest that suspected spy balloons have been regular visitors over the islands. Citing defense sources, Fox News reported that a suspected Chinese spy balloon crashed near Hawaii as recently as four months ago, and CNN obtained a U.S. Air Force report from April titled “People’s Republic of China High-Altitude Balloon,” which found that a Chinese spy balloon had “circumnavigated the globe” in 2019 at an altitude of roughly 65,000 feet and “drifted past Hawaii and across Florida before continuing its journey.”