Police officers inspect the roof of Prime Minister Shinzo Abe's official residence in Tokyo April 22, 2015. [Photo/Agencies]

TOKYO - Japanese authorities were investigating Wednesday after a small drone landed on the roof of the prime minister's office.

No injuries or damage were reported from the incident, and Prime Minister Shinzo Abe was in Indonesia to attend an Asia-African conference.

Police said it was not immediately known who was responsible for the drone. They were investigating the possibility it had crashed during a flight.

It was not clear when the drone landed. It was discovered Wednesday by an official who was taking new employees on a tour of the prime minister's office in central Tokyo, according to media reports.

Video from public television broadcaster NHK showed dozens of police officers and officials around the drone, which was covered by a blue tarp.

The drone was about 50 centimeters (1.7 feet) in diameter and had four propellers, carrying a small camera and something that looked like a flare, NHK said. It was also decorated with a symbol that warns of radioactive material.

Small drones are becoming increasingly popular in Japan and are often used for performances, aerial filming and other purposes. But they have raised safety and privacy concerns.

Japanese aviation laws have no restrictions for flying unmanned equipment at or below 250 meters (820 feet) above ground except for flight routes.