Japan is now immediately scrambling fighter jets against all Chinese military aircraft taking off from an air base in Fujian Province, as tensions continue between the two countries over the Senkaku Islands, government sources said Saturday.

Japan's Air Self-Defense Force planes have also been flying above the East China Sea from sunrise to sunset every day to monitor Chinese military aircraft moves, the sources said.

File photo taken in September 2012 shows the Japan-controlled Senkaku Islands in the East China Sea. Taiwan and China claim the uninhabited islands as their own. (Kyodo)

Before Japan reviewed its policy early last year, it used to scramble fighter jets against Chinese military aircraft approaching its airspace.

China had sent fighter jets to near the Senkakus from Zhejiang Province but it moved the location of their take-off to the air base, much closer to the islands disputed by Beijing, according to the sources.

The distance between the air base and the Japan-controlled islands is about 380 kilometers, where Chinese J-11 fighter jets can travel in about 20 minutes.

Meanwhile, the distance between the ASDF's base in the Okinawa prefectural capital Naha, from which Japan scrambles jets against Chinese military aircraft, is about 410 km, requiring a travel time of about 25 minutes for the air force's F-15 fighters.

The ASDF now needs to immediately respond to Chinese fighters when they leave from the air base and prevent them from entering Japan's airspace, the sources said.

By combining information provided by the sources, the ASDF has set a defense line at a latitude of 27 degrees north, to block Chinese military aircraft's approach near the islands, which are located between latitudes of 25 and 26 degrees north.

The ASDF used to respond to one Chinese military plane with two fighter jets. But it now does so with four fighters, they said.

Japan scrambled fighter jets against Chinese military aircraft 638 times in fiscal 2018 and 675 times in the previous fiscal year through March, according to the Defense Ministry.