China on Wednesday warned that US President Donald Trump's "Golden Dome" missile shield system "undermines global stability" after he announced US$25 billion in initial funding for the plan.

"This undermines global strategic balance and stability. China expresses serious concern over this," Foreign Ministry spokeswoman Mao Ning told a regular briefing.

"The United States puts its own interests first and is obsessed with seeking its own absolute security, which violates the principle that no country's security should come at the expense of others.

"(The plan) heightens the risk of space becoming a battlefield, fuels an arms race, and undermines international security.

"We urge the United States to abandon the development and deployment of a global missile defence system as soon as possible."

Trump on Tuesday unveiled new details on the missile shield system to protect the country against attacks, saying it should be operational in about three years.

Pentagon chief Pete Hegseth, speaking alongside the US president, said the system is aimed at protecting "the homeland from cruise missiles, ballistic missiles, hypersonic missiles, drones, whether they're conventional or nuclear."

Trump announced US$25 billion in initial funding, which he said could eventually cost a total of some US$175 billion. (AFP)