China has warned the U.S. to stop supporting Taiwan or suffer "serious consequences."

The U.S. must stop enhancing its relationship with Taiwan and must handle Taiwan-related matters carefully and properly to prevent "serious harm to China-U.S. collaboration" in peace and stability across the Taiwan Strait, China's Foreign Ministry spokesperson Zhao Lijian said.

Zhao said Taiwan must not become too submissive and dependent on foreign support. China insists Taiwan is part of a "One China" and said it would be forced to respond militarily if Taiwan declared independence.

Continuing friction between China and the U.S. intensified after U.S. Health Secretary Alex Azar visited Taiwan and hailed relations between it and the U.S. - prompting China to warn the U.S. not to "play with fire" Wednesday.

Azar ended a three-day visit to Taiwan with a meeting with Taiwan leader Tsai Ing-wen. The two discussed Taiwan's efforts to fight COVID-19 - which the U.S. diplomat described as some of the most "successful" in the world.

China was incensed by the U.S. delegation. China criticized Azar's visit saying it went against official exchanges between Taiwan and the Americans. Zhao said the U.S. must be realistic and understand that those who "play with fire will get burned."

China and the U.S. have been at odds over Taiwan since President Donald Trump was elected in 2016 and he became the first U.S. leader to accept a telephone call from a president of Taiwan since 1979.