A fleet of six Y-20 cargo planes of the Chinese People's Liberation Army Air Force was reportedly seen in Serbia on Saturday. Observers said this could be the largest overseas operation conducted by domestic Chinese large transport planes to date, proving Beijing's strategic transport capabilities.

The aircraft were observed on commercial flight trackers, and they were reportedly first spotted over Turkey. Local residents took photos of the Chinese aircraft that were said to have landed at Nikola Tesla Airport in Belgrade, Serbia. Later, the aircraft flew in Turkish airspace once again on their flight back home.

Beijing is yet to make an official announcement on the mission, though the Global Times was told that the Y-20s did go to Serbia as reported.

Chinese military observers commented on the flight by saying such a vast amount of Y-20s, renowned for their size, could mark an unprecedented overseas operation for China.

A Chinese military aviation expert said the mission set a new record for Y-20 aircraft deployed simultaneously, as it is very rare to see that amount of Y-20s flown at the same time.

The mission is a reflection of the significant boost in the Chinese Air Force's capabilities in terms of long-range strategic transport, not to mention the large transport aircraft's logistics support and maintenance capabilities in intercontinental flights, expert Fu Qianshao said.

"It is more difficult to organize a large fleet featuring six Y-20s compared with only one or two of the aircraft," another Chinese military expert, Song Zhongping, told the Global Times.

Song also highlighted the high level of communication that Beijing had with several other countries, as the Y-20s had to cross several countries before reaching their destination in Serbia.

The mission to Serbia, however, remains unknown, though US news site The Drive speculated that the aircraft could be delivering the FK-3, a version of the Chinese HQ-22 SAR missile system made for export.