Taiwan Photo: Unsplash

 A charter plane carrying Taiwan  personnel from "coast guard and defense authority" was reportedly rejected and forced to return by the management authority at Hong Kong's flight information region (FIR) in the South China Sea on Thursday, which observers said reflects the one-China principle and cross-Straits tensions.

The plane, operated by Taiwan's UNI Airways, was on its way to the Dongsha islands, but ordered to return to Taiwan by the Hong Kong authority, Taiwan media reported, citing Taiwan's civil aeronautics authorities, adding it was the first time it happened.

The flight was informed by Hong Kong's flight information region authority that there was "dangerous activity 26,000 feet below the flying region" when the flight was near the connection point of Taiwan and Hong Kong's flight information regions, Taiwan's United Daily News reported, quoting the island's traffic authority.

Citing the civil aviation rules, United Daily News reported when a flight passed the KAPLI checkpoint on the G86 international airway, it should report to the Hong Kong FIR management center and accept its direction.

Some Taiwan media said the related activity could be the drill of the People's Liberation Army in nearby waters.

Taiwan is part of China and should obey the rules of Chinese authorities, and Taiwan aircrafts should declare their route before flying, Song Zhongping, a Chinese military expert and TV commentator, told the Global Times on Thursday. "This Taiwan plane did not report its flight route, so it was forced to return."

"It reflects the one-China principle," Song said. The one-China principle could be implemented in many ways, such as issues on the "middle line" of the Taiwan Straits, and the air control regions.

"Hong Kong is a special administrative region of China. The Hong Kong-Taiwan relation is under the direction of the Chinese central government. It is justified for Hong Kong to reject the Taiwan island's flight," Zhang Wensheng, a deputy dean of the Taiwan Research Institute at Xiamen University, told the Global Times on Thursday.

Zhang added that when cross-Straits relations were more moderate, there would usually be tacit agreements between military aircraft from the two sides, as flying to Dongsha or Kinmen, Taiwan flights can hardly avoid entering the mainland's FIR. 

According to the International Civil Aviation Organization, most countries or regions divide the airspace under their jurisdiction into several flight information regions, including the airspace above the adjacent high seas.

The United Daily News said that the charter flight brings members of sea patrol and defense departments of Taiwan, and runs regularly between the island of Taiwan and Dongsha islands.