US President-elect Donald Trump has posted a series of tweets criticising China for its monetary policy and its operations in the South China Sea.
“Did China ask us if it was OK to devalue their currency” and “build a massive military complex?” he asked. “I don’t think so!”
Last week Mr Trump risked a diplomatic rift with China by speaking directly with Taiwan’s president.
The highly unusual move saw China lodge a complaint with the US.
The US has previously criticised China’s yuan devaluation, saying it unfairly favours Chinese exporters.
Mr Trump’s phone call with Taiwan’s President Tsai Ing-wen was thought to be the first time a US leader or leader-in waiting has spoken to a Taiwanese leader since 1979, the year formal ties were severed.
The White House has said the phone call did not signal a shift in its decades-long “One China” policy stance, which considers Taiwan to be part of China.
Vice President-elect Mike Pence has tried to downplay the call.
Beijing lodged a “solemn representation” with Washington, where it urged the US to “cautiously and properly handle” the issue of Taiwan, according to Chinese state media.
Taiwan sees itself as an independent state but Beijing considers it as a breakaway province.
It has hundreds of missiles pointing towards Taiwan, and has threatened to use force if Taiwan formally declares independence.