Beijing's naval forces appear to be holding a rare twin carrier exercise in the South China Sea this week amid tensions with U.S. ally the Philippines over disputed territory.

Satellite imagery captured on Tuesday showed at least eight warships sailing in a dense formation. They included the Chinese aircraft carrier Shandong and one Type 075 amphibious assault ship, while at least two 11,000-ton Type 055 guided-missile destroyers provided escorts, according to open-source analysts on X (formerly Twitter).

China's Shandong aircraft carrier and Type 075 landing helicopter dock conducted a rare exercise in the South China Sea today. pic.twitter.com/cPxFp7SOon

— Duan Dang (@duandang) July 2, 2024

The Chinese naval formation was spotted about 50 miles northeast of Woody Island, which China calls Yongxing, the largest of the Beijing-controlled Paracel Islands in the South China Sea, claimed by Vietnam and others.

China has built an airstrip, hangars, and deployed air defense missile batteries on the heavily militarized territory, according to the Asia Maritime Transparency Initiative, part of the Center for Strategic and International Studies think tank in Washington, D.C.

The Shandong is China's first domestically built carrier and the second in service. It is homeported in Hainan, a Chinese island province facing the South China Sea.

Japan's Defense Ministry said the Shandong and other surface combatants conducted exercises in the Philippine Sea—beyond the so-called first island chain—from late October to early November last year.

Type 075 helicopter carrier, which NATO calls the Yushen class, is a naval platform that modernizes China's amphibious assault capability.

It is slightly smaller than the U.S. Navy's 41,500-ton Wasp-class amphibious assault ship, with a displacement of 35,000 tons. There are currently three Type 075s in service, while a fourth was launched in December.

China's show of strength in the contested waters was in addition to its reliance on its coast guard fleet to assert sovereignty over disputed islands.

The Philippine coast guard said last week it was able to track the movements of the Chinese coast guard cutter 5901, also known as "The Monster," for the past 10 days, thanks to unspecified technology under Canada's Dark Vessel Detection program.

Displacing 12,000 tons, the Zhaotou-class 5901 is the world's largest coast guard cutter, larger even that the U.S. Navy's 9,800-ton Ticonderoga-class cruisers and its 9,900-ton Arleigh Burke-class destroyers.

The 5901 departed from Hainan on June 17 and "directly encroached upon the territorial waters" of Philippine-occupied features in the Spratly Islands archipelago, Philippine coast guard spokesperson Jay Tarriela said on X.

Newsweek could not independently verify the authenticity of the tracking data.

Using Canada's Dark Vessel Detection technology, the Philippine Coast Guard was able to track the movement of the Chinese Coast Guard's monster ship (CCG 5901) for the past ten days.

On June 17th, CCG 5901 departed from Hainan and directly encroached upon the territorial… pic.twitter.com/6oqe7bojto

— Jay Tarriela (@jaytaryela) June 27, 2024

In response to the reported presence of the Chinese carrier and the China coast guard "monster" ship in the South China Sea, the Philippine navy said it was monitoring the country's maritime domain.

"They are authorized under UNCLOS either through freedom of navigation or right of innocent passage," Philippine navy spokesperson Roy Vincent Trinidad said, referring to the United Nations Convention on the Law of the Sea.