China has expanded its presence in the contested South China Sea by switching on a lighthouse atop a reconstructed reef also claimed by Vietnam and the Philippines, state media said.

The 55-meter-high (180-foot) facility on Subi Reef in the Spratly chain contains technology to monitor passing ships, the official Xinhua news agency reported late Tuesday.

China claims virtually all the South China Sea despite conflicting claims by Brunei, Malaysia, Vietnam, Taiwan and the Philippines. It has constructed artificial islands in the area in recent months as it asserts its claims.

China has turned Subi Reef -- known as Zhubi in China -- into an artificial island in the past year, satellite photos have shown, reclaiming nearly 400 hectares (988 acres) of land.

The island-building has been condemned by neighbours and the United States, but Beijing insists it is aimed at helping with maritime search and rescue.

Chinese transport officials held a ceremony on Subi on Tuesday, Xinhua said. Pictures showed men in white shirts beside the towering structure next to a sign reading "Lights-on ceremony".

Washington regularly accuses Beijing -- which says it has built runways and deployed unspecified weapons to the islands -- of militarising the area.

Beijing denies the accusations and says US patrols have ramped up tensions.

Citing an obligation to uphold freedom of navigation, Washington last year sent the USS Lassen to sail past Subi Reef, a move which angered Beijing.

Xinhua reported last year that China would build two 50-metre-tall lighthouses on the Cuarteron and Johnson South reefs in the Spratly islands, which are also claimed by Vietnam and the Philippines.

The state-run China Daily newspaper reported in 2014 that Beijing would build five new lighthouses in the South China Sea's Paracels chain.