China says a war with the United States would be a disaster for the world as it warns Washington not to meddle in Taiwan and the South China Sea.

Defense Minister Wei Fenghe warned Sunday that China will “resolutely take action” and "fight at all costs" to defend its sovereignty over self-ruled Taiwan and South China Sea waters.

US President Donald Trump’s administration stepped-up support for secessionist forces in Taiwan and US Navy sailings through the Taiwan Strait that separates the island from mainland China have incensed China.

Wei told the Shangri-La Dialogue in Singapore, Asia’s premier defense summit, that China would “fight to the end” if anyone tried to interfere in Taiwan, which Beijing considers a sacred territory to be taken by force if necessary.

"We will strive for the process of peaceful reunification with utmost sincerity and greatest efforts but we make no promise to renounce the use of force," Wei said. 

The United States, like most countries, has no formal ties with Taiwan, but is its strongest backer and main source of weapons.

“China must be and will be reunified. We find no excuse not to do so. If anyone dares to split Taiwan from China, the Chinese military has no choice but to fight at all costs, at all costs, for national unity,” Wei said.

His remarks came a day after Pentagon chief Patrick Shanahan said in Singapore that the US was investing heavily in the Indo-Pacific region with the aim of confronting China.

"The Indo-Pacific is our priority theater. We are where we belong. We are investing in the region," he said.

"We want to ensure no adversary believes it can successfully achieve political objectives through military force," Shanahan said, adding the US would no longer “tiptoe” around Chinese activities in Asia. 

China-US ties have become increasingly strained due to a bitter trade war. Tensions have further risen over the sailing of American warships and warplanes near a chain of islands in the South China Sea which Beijing considers its own. 

US �playing with fire� on Taiwan: China warns

China says the United States is “playing with fire” by a series of actions it has taken in the Taiwan Strait in support of the self-ruled island’s secession bid.

"Some countries from outside the region come to the South China Sea to flex muscles in the name of freedom of navigation," Wei said in a clear reference to the United States.

Washington has long challenged China�s sovereignty claims over most of the strategic waters, which act as gateway to trillions of dollars in annual maritime trade.

The fresh war of words came just after Wei and Shanahan met on the sidelines of the conference Friday and agreed to improve communication and deepen exchanges and cooperation between their militaries.

Wei said on Sunday a conflict or war between the United States and China would have wide-reaching effects. “It takes two to cooperate but only one to start a fight,” he said.

“We hope that the US side will work with us towards the same goal, follow the principles of non-conflict, non-confrontation, mutual respect and win-win cooperation, and steer the China-US relations in the right direction.”