“If the Americans draw their missiles and position-guided ammunition on to the target zone on China's territory, I think we will have to respond with nuclear weapons,” Zhu Chenghu, a major general in the People's Liberation Army, said at an official briefing.

Mr Zhu, who is also a professor at China's National Defence University, was speaking at a function for foreign journalists organised, in part, by the Chinese government. He added that China's definition of its territory includes warships and aircraft.

“If the Americans are determined to interfere [then] we will be determined to respond,” Mr Zhu said. “We Chinese will prepare ourselves for the destruction of all of the cities east of Xian. Of course the Americans will have to be prepared that hundreds. . . of cities will be destroyed by the Chinese.” Mr Zhu is a self-acknowledged “hawk” who has warned previously that China could strike the US with long-range missiles. But his threat to use nuclear weapons in a conflict over Taiwan is the most specific by a senior Chinese official in nearly a decade.

Rick Fisher, a former senior US congressional official and an authority on the Chinese military, said the specific nature of the threat “is a new addition to China's public discourse”.

China's official doctrine has called for no first use of nuclear weapons since its first atomic test in 1964. But Mr Zhu is not the first Chinese official to refer to the possibility of using such weapons first in a conflict over Taiwan.

Chas Freeman, a former US assistant secretary of defence, said in 1999 that a PLA official had told him China could respond in kind to a nuclear strike by the US in the event of a conflict with Taiwan.

“In the end you care more about Los Angeles than you do about Taipei,” Mr Freeman quoted this official as saying. The official is believed to have been Xiong Guangkai, now the PLA's deputy chief of general staff.

The rationale for the new threats is unclear. China's Ministry of Foreign Affairs could not be reached for comment.

Mr Zhu, who has risen from the rank of colonel over the past five years, insisted he was expressing his personal views, and that they did not represent the policy of the Chinese government. Nor was he anticipating war between China and the US.

But he said that, because China did not have the capability to fight a conventional war against the US, the threat to escalate might be the only way to stop a war.

His comments could provide insight into the thinking among some in the PLA amid growing anxiety in Washington about its capabilities. Last month, Donald Rumsfeld, defence secretary, voiced concern about China's military build-up.