President Lai Ching-te's office made the remarks after a report published by a US think tank said Chinese state oil giant CNOOC had 12 structures in Taiwan's claimed exclusive economic zone (EEZ) near disputed Pratas Island.

Taiwan controls Pratas in the northern part of the South China Sea but Beijing also claims the island, along with most of the strategic waterway.

"In recent years, China has been deploying oil and gas exploration platforms and other fixed structures within the exclusive economic zones and continental shelves of South Korea, Japan, our country and other countries surrounding the South China Sea," Lai's office said in a statement.

"This not only violates international legal norms such as the United Nations Convention on the Law of the Sea (UNCLOS), but also seriously undermines the international order and poses uncertain risks to regional stability," it said, calling on China to "immediately stop" the illegal activities.

Taiwan, whose claim to statehood is recognised by 11 countries and the Vatican, is not a member of the United Nations nor a party to UNCLOS.

The report published by The Jamestown Foundation on Tuesday said CNOOC had "seven rig structures, three floating production storage and offloading vessels, and two semi-submersible oil platforms" near Pratas.

One of the semi-submersible rigs was moved "deep into Taiwan's claimed EEZ" in July and it was only about 30 miles (48 kilometres) from Pratas's restricted waters, the report said.

"Oil rigs now constitute part of Beijing's multidimensional campaign to undermine Taiwan's sovereignty, which also includes cognitive, legal, and economic warfare," said the report, whose lead author is Andrew Erickson, a professor at the US Naval War College's China Maritime Studies Institute.

The structures had been in the waters "since at least May 2020" and could be used to "facilitate" a blockade, bombardment or an invasion against Pratas or Taiwan, the report said.

China claims Taiwan is part of its territory and has threatened to use force to bring the democratic island under its control.

Beijing has ramped up pressure in recent years, deploying military aircraft and warships around Taiwan on a near-daily basis.