Washington: The new US administration of President Donald Trump has vowed that the United States would prevent China from taking over territory in international waters in the South China Sea, something Chinese state media has warned would require Washington to "wage war".

The comments at a briefing from White House spokesman Sean Spicer on Monday signalled a sharp departure from years of cautious US handling of China's assertive pursuit of territory claims in Asia, just days after Mr Trump took office on Friday.

"The US is going to make sure that we protect our interests there," Mr Spicer said when asked if Mr Trump agreed with comments by his secretary of state, Rex Tillerson, on January 11 that China should not be allowed access to islands it has built in the contested South China Sea.

"It's a question of if those islands are in fact in international waters and not part of China proper, then yeah, we're going to make sure that we defend international territories from being taken over by one country," he said.