China claims self-ruled Taiwan as part of its territory and relations have soured since Taiwan's independence-leaning President Tsai Ing-wen came to power in 2016, with Beijing ratcheting up military and political pressure on the island.

Taiwan's defence ministry said in a statement that 68 Chinese aircraft and 10 naval vessels were detected near the island between Wednesday morning and Thursday morning.

Taipei had already said some of those planes and warships were heading to an unspecified area of the Western Pacific to "conduct joint sea and air training" with China's Shandong aircraft carrier.

The Shandong, one of two operational aircraft carriers in the Chinese fleet, was detected Monday around 60 nautical miles (110 kilometres) southeast of Taiwan heading into the Western Pacific, Taipei authorities said.

Japan's defence ministry also said Wednesday its navy had detected six ships -- including frigates, destroyers, one fast combat support ship and the Shandong -- sailing through waters some 650 kilometres (400 miles) south of Miyakojima island, east of Taiwan.

It also confirmed that jets and helicopters had been detected taking off and landing from the Shandong.

- 'Grey zone' -

Taipei warned this week that China was stepping up "grey zone" activities around the island, accusing Beijing of seeking to raise regional tensions and pressure the territory while avoiding all-out conflict.

China's military "has been tasked to develop capabilities to take over Taiwan", one expert said.

"Those military exercises are aimed at developing and practising those capabilities," Bonnie Glaser, a China expert at Washington DC's German Marshall Fund.

"We should expect its trend to continue, with growing pressure on Taiwan."

China has not commented officially on any drills being conducted in the Western Pacific.

However, its Eastern Theatre Command, which organises drills around Taiwan, said Wednesday an "aviation unit" had carried out training "recently" in a range of "thousands of kilometres".

It did not mention Taiwan.

China said last week its troops were "on constant high alert" after two ships belonging to the United States and Canada sailed through the Taiwan Strait.

The US Navy said the ships were the Arleigh Burke-class guided-missile destroyer USS Ralph Johnson and HMCS Ottawa, and that the transit "demonstrates the commitment of the United States and our allies and partners to a free and open Indo-Pacific", another term for the Asia-Pacific region.

The United States and Western allies have increased "freedom of navigation" crossings of both the Taiwan Strait and the disputed South China Sea to reinforce that both are international waterways, angering Beijing.

China conducted military exercises in April to simulate the encirclement of Taiwan after Tsai met US House Speaker Kevin McCarthy in California.