The Maritime Self-Defense Force on Sunday morning spotted China’s only aircraft carrier, the Liaoning, cruising into the Western Pacific Ocean for the first time via the waterway between Okinawa and Miyakojima Island, the Defense Ministry said.

The Liaoning, accompanied by three guided missile destroyers and two frigates, was spotted about 110 km northeast of Miyakojima in Okinawa Prefecture heading southeast at around 10 a.m., the ministry said.

This is the first time the Liaoning has been confirmed as entering the Pacific Ocean, ministry officials said.

The exercise is seen as part of the Chinese navy’s effort to expand its operational area to the Pacific Ocean.

The flotilla was initially spotted by a P-3C patrol plane from the Maritime Self-Defense Force, the ministry said.

The MSDF also reported that a Z-9 patrol helicopter took off from one of the frigates and flew around an area of about 10 to 30 km southeast of Miyakojima, the ministry said.

China’s official Xinhua News Agency reported Saturday that a naval formation including the Liaoning was headed to the western Pacific the same day for an open-sea training exercise.

“This exercise is being carried out in accordance with annual exercise plans,” the Chinese navy said in a statement that was also carried on the front page of the official People’s Liberation Army Daily.

The Liaoning was converted from a Soviet-built hulk that China purchased from Ukraine in 1998. After undergoing extensive refitting in Dalian, it was commissioned in September 2012 as China’s first aircraft carrier.

The Chinese military conducted its first ever live-fire drills using an aircraft carrier in the Bohai Sea close to the Korean Peninsula this month, and has more recently been operating in the East China Sea.

The navy showed pictures of the drills on its official microblog, including the launching of J-15 carrier-borne fighter jets under the watch of its naval chief, Wu Shengli.

They also conducted aerial refueling and air combat exercises on Thursday, the navy said.

China’s growing military presence, especially in the disputed South China Sea, has fueled concern in Japan and the United States. The U.S. has accused Beijing of militarizing maritime outposts and holding regular air and naval patrols to ensure freedom of navigation in the area.

The Western Pacific exercise comes amid new tension over self-ruled Taiwan following U.S. President-elect Donald Trump’s telephone call with Taiwan’s president, which upset Beijing.

The People’s Liberation Army Air Force conducted long-range drills this month above the East and South China Seas that rattled Japan and Taiwan. China said those exercises were also routine.

The Soviet-built Liaoning has participated in previous exercises, including some in the South China Sea, but China is years away from perfecting the carrier operations that the United States has practiced for decades.

Last December, the defense ministry confirmed China was building a second aircraft carrier, but its launch date is unclear. The aircraft carrier program is a state secret.

Beijing could build multiple aircraft carriers over the next 15 years, the Pentagon said in a report last year.

Successful operation of the Liaoning, originally built in Ukraine for the Soviet navy, is the first step in what the state media and some military experts say will be the rollout of Chinese-built aircraft carriers by 2020.