China has warned Taiwan that any attempt to seek independence "means war".
The warning comes days after China stepped up its military activities and flew warplanes near the island.
It also comes after new US President Joe Biden reaffirmed his commitment to Taiwan, and set out his stance in Asia.
The US has called China's latest warning "unfortunate", adding that tensions did not need to lead to "anything like confrontation".
China sees democratic Taiwan as a breakaway province, but Taiwan sees itself as a sovereign state, with its own constitution, military, and elected leaders.
Analysts say Beijing is becoming increasingly concerned that Taiwan's government is moving the island towards a formal declaration of independence and it wants to warn President Tsai Ing-wen against taking steps in that direction.
President Tsai, however, has repeatedly said that Taiwan is already an independent state, making any formal declaration unnecessary.
On Thursday, Chinese defence ministry spokesman Wu Qian defended the recent military activities near Taiwan, saying they were "necessary actions to address the current security situation in the Taiwan Strait and to safeguard national sovereignty and security".
"They are a solemn response to external interference and provocations by 'Taiwan independence' forces," he added.
"We warn those 'Taiwan independence' elements - those who play with fire will burn themselves, and Taiwan independence means war."
China and Taiwan: The basics
China and Taiwan have had separate governments since the end of the Chinese civil war in 1949. Beijing has long tried to limit Taiwan's international activities and both have vied for influence in the Pacific region
Tensions have increased in recent years and Beijing has not ruled out the use of force to take the island back
Although Taiwan is officially recognised by only a handful of nations, its democratically elected government has strong commercial and informal links with many countries
Like most nations, the US has no official diplomatic ties with Taiwan, but a US law does require it to provide the island with the means to defend itself
The US responded later on Thursday.
"We find that comment unfortunate," Pentagon press secretary John Kirby told reporters, in the first statement by the new administration on China-Taiwan relations.
Mr Kirby added that the Pentagon "sees no reason why tensions over Taiwan need to lead to anything like confrontation".
The new US administration is expected to maintain pressure on China over a wide range of issues including human rights, trade disputes, Hong Kong and Taiwan, amid the deteriorating relationship between the two powers.
Taiwan's Mainland Affairs Council, meanwhile, said China should "not underestimate" the island's determination to defend its sovereignty and uphold freedom and democracy.