[HONG KONG] Japan scrambled jets on Sunday after a fleet of Chinese aircraft flew into a strategically important strait near disputed islands in the East China Sea.

Japan sent out the jets after eight of the Chinese planes crossed back and forth over waters between Okinawa's main island and Miyako Jima island near Taiwan, the Defence Ministry in Tokyo said in a statement. Two of the planes may have been fighter jets, the ministry said.

While the Chinese planes didn't cross into Japanese airspace, it was the first time that Japan saw Chinese fighter jets in the Miyako Strait, Chief Cabinet Secretary Yoshihide Suga told reporters in Tokyo on Monday.

He said that Japan rejected China's Air Defence Identification Zone that encompasses islands known as Senkaku in Japan and Diaoyu in China.

"We cannot accept the implication that the airspace over the Senkaku islands, which are part of our territory, belongs to China," Mr Suga said.

The People's Liberation Army Air Force sent a fleet of 40 aircraft - comprising H-6K bombers, Su-30 fighters and air tankers - on what it called a "routine" drill through the Miyako Strait on route to the West Pacific for exercises, a defence ministry statement said.

It quoted Air Force spokesman Shen Jinke speaking from "a certain airport in East China."

The fleet performed surveillance, sudden assault and aerial refueling exercises, as well as "routine warning patrols" in China's Air Defense Identification Zone in the East China Sea, according to Mr Shen.

The exercises stemmed from the need "to safeguard national sovereignty, protect national security and maintain peaceful development," Mr Shen said.

Last May, the PLA air force said it had flew warplanes through the Miyako Strait towards the West Pacific for drills.

The size of the fleet over the weekend was uncommon, said Xu Guangyu, senior adviser at Beijing-based research group the China Arms Control and Disarmament Association.

"It's not been seen often in the past," said Mr Xu, a retired PLA major general.

"The exercise aimed at enhancing open sea combat ability, and it's part of the military's reform to familiarise the troops with a battlefield environment. Americans and Russians both routinely conduct this type of exercise."

The movements in the East China Sea underscore the frosty relationship between Asia's two biggest economies.

One of the thorniest issues is the long-running dispute over sovereignty of the tiny islands.

In a speech in Washington earlier this month, Japanese Defense Minister Tomomi Inada criticised China for its increasingly aggressive behaviour in both the East China Sea and the South China Sea.

She singled out Beijing for its reclamation of land around maritime features and expressed support for the US Navy's freedom of navigation operations.

BLOOMBERG