China this weekend sent a flight of six nuclear-capable bombers over disputed islands near Okinawa, warning Japan such stand-offs will become "the new norm".
Beijing announced at the weekend that its H6K bombers had flown "several" long-range drills over the Bashi Channel and Miyako Strait during the past week.
The strategic Miyako strait sits between the Sakishima islands - scene of fierce fighting during the last days of World War II by the British Pacific Fleet - and Okinawa, linking mainland Japan with the northern tip of Taiwan.
The equally significant Bashi Channel is a waterway linking the South China Sea and the Pacific between Taiwan and the Philippines.
Whoever controls the waterways has access to rich fish stocks, underwater resources - and military control over access to shipping lanes of vital importance to regional powers Japan and China.
'Get used to it'
"China's air force over the past week conducted multiple drills far out at sea, with H-6K bombers and many other types of aircraft flying through the Bashi Channel and Miyako Strait, testing actual battle capabilities over the sea," a spokesman told the state-run CGTN news service.
The flight of six H6K bombers passed through the Miyako Strait on Thursday as part of "routine exercises", a Beijing Defence Ministry official said.
Japan scrambled fighters from nearby Okinawa and closely observed the Chinese aircraft, which remained in international airspace.
A Japanese defence force spokesman noted, however, that the Chinese action was "unusual".
"It is legitimate for Chinese military planes to fly through the strait, and more similar training will be conducted on the high seas as needed," spokesman Ren Guoqiang Guoqiang told Chinese media.
"The parties concerned don't need to overact and make a great fuss about it," he added. "They will feel better after getting used to such drills."
First island chain
China has in recent months sought to assert its military strength and its ability to reach into the Pacific, sending ships - including its aircraft carrier Liaoning - into politically sensitive waters around Taiwan and Okinawa.
In March this year, China surged a large-scale force of 13 naval fighter and bomber aircraft through the same Mikayo Strait, startling Tokyo into declaring it would keep an eye on China's 'expanding and increasing' actions.
Japan last year doubled the number of fighter jets based in Okinawa to counter a series of Chinese 'probes' in September, November and December.
It's naval presence in the Indian Ocean has also been increasing, with India expressing alarm at the presence of submarines and up to 13 warships operating in waters between Singapore and the Horn of Africa. Last week, it sent its first detachment of troops to establish a naval base in Djibouti.