Australian, Japanese and U.S. air force planes are dropping food and toys on remote atolls in the Pacific as part of the U.S. military's longest-running humanitarian relief mission.

The packages will support 20,000 people across 56 islands in Micronesia, the Mariana Islands and Palau.

The U.S. Air Force says the annual Operation Christmas Drop began in 1952 when a Guam-based air crew noticed residents on a small Micronesian island waving at them as they flew overhead. The crew gathered items from the plane and dropped them with a parachute.

It's a feel-good mission that also helps the U.S. achieve political aims.

Australia and Japan are joining the mission for the first time. The U.S. has been deepening three-way cooperation with the two close allies as it keeps an eye on China's growing military.