The Foreign Ministry in Beijing on Monday denied China was testing nuclear weapons.

"China has always adhered to the path of peaceful development, pursued a policy of no first use of nuclear weapons, upheld a self-defence nuclear strategy and abided by its commitment to suspend nuclear testing," Foreign Ministry spokeswoman Mao Ning said.

She added that China hopes the United States will "take concrete actions to safeguard the international nuclear disarmament and non-proliferation regime and maintain global strategic balance and stability".

The ministry's response comes after US President Donald Trump alleged on Sunday that countries including Russia and China have been conducting secret underground nuclear tests, and that Washington would follow suit.

Trump's energy secretary on Sunday downplayed that the US was planning to set off a nuclear explosion.

"I think the tests we're talking about right now are system tests. These are not nuclear explosions," Chris Wright said in a Fox News interview. (AFP)