China has again sent its Liaoning aircraft carrier through the Miyako Strait — a key strategic gateway into the Pacific for Beijing that separates Okinawa’s main island from Miyako Island.

The Defense Ministry said late Friday that the Maritime Self-Defense Forces had initially detected the carrier about 350 kilometers southwest of Nagasaki Prefecture’s Danjo Islands on Wednesday and tracked the vessel, as well as an accompanying flotilla of three other ships, sailing southward through the 150-nautical-mile-wide strait into the Western Pacific Ocean on Thursday.

The ministry said the Chinese flotilla included the Chinese Navy’s state-of-the-art guided-missile Type 055 destroyer, a Type 054 frigate and a Type 901 fast combat support ship.

It said Japanese vessels, including the Izumo — which along with its sister ship, the Kaga, is the MSDF’s largest vessel — had monitored the Liaoning-led flotilla, which later conducted flight operations involving helicopters and fighter jets in the East China Sea and Pacific Ocean.

The vessels and aircraft did not enter Japanese territorial waters or airspace.

The Chinese ships’ drills in the Pacific are likely intended to check military activities in the waters by the U.S., Japan and Taiwan.

The Liaoning, a refurbished Soviet vessel, is one of China’s two active carriers. The other is the Shandong, the country’s first domestically produced carrier.

Earlier this month, the Type 055 destroyer conducted “intensive anti-submarine drills” in an apparent warning to the U.S. Navy, Chinese state-run media said.

In April, the Liaoning carrier and other vessels sailed through the Miyako Strait and sent aircraft near the Japanese-controlled Senkaku Islands, which are also claimed by China, where they are known as the Diaoyu.

The move was seen as a warning to Japan after “repeated wrong statements” on the tiny uninhabited islands in the East China Sea, according to state media.