Chinese and Russian sailors are spending Christmas in the East China Sea this year. A handful of ships from the two countries are taking part in maritime cooperation, the latest in a series of military drills the two countries held this year.

Russia’s Ministry of Defense said on Monday four vessels are taking part in the drills, which run from Dec. 21-27.  Russia is sending the flagship of its Pacific Fleet, the Varyag missile cruiser. A frigate and two corvettes will accompany the Varyag.

China said it was sending six ships to the drills. According to reporting by the South China Morning Post, however, Japan said it spotted nine Chinese navy vessels sailing in the region, including the Liaoning aircraft carrier. Videos posted to social media from aboard the carrier show planes practicing takeoff and landing drills.

Russia’s Ministry of Defense said the mutual exercises between China and Russia will “strengthen naval cooperation,” as well as “maintain peace and stability in the Asia-Pacific Region.”

The joint naval exercises have taken place every year since 2012 and are just one of many joint military exercises the two countries held this year.

Before Russia invaded Ukraine in February, Beijing and Moscow signed a “no limits’ strategic partnership. However, Chinese President Xi Jinping has criticized Vladimir Putin’s threats to use nuclear weapons.

Reuters contributed to this report.