The policy shift was first reported by Bloomberg News and confirmed by the US government agency.

"NASA has taken internal action pertaining to Chinese nationals, including restricting physical and cybersecurity access to our facilities, materials, and network to ensure the security of our work," NASA press secretary Bethany Stevens told AFP Wednesday.

According to Bloomberg, Chinese nationals had previously been allowed to work as contractors or students contributing to research, although not as staff.

But on September 5 several individuals told the outlet they were suddenly locked out of IT systems and barred from in-person meetings. They spoke on condition of anonymity.

The move comes amid escalating anti-China rhetoric under President Donald Trump's administration. The United States and China are competing to send crews to the Moon.

The US Artemis program, a follow-up to the Apollo landings from 1969-1972, is targeting a 2027 landing but has suffered cost overruns and delays.

China, by contrast, aims to land its "taikonauts" by 2030 under its program, and has recently been more successful at meeting deadlines.

"We're in a second space race right now," NASA's acting administrator Sean Duffy told reporters Wednesday, speaking at a news conference related to discoveries made with a US rover on Mars.

"The Chinese want to get back to the Moon before us. That's not going to happen. America has led in space in the past, and we are going to continue to lead in space in the future."

China is also seeking to become the first country to return a sample from the Martian surface, with a robotic mission slated to launch in 2028 and bring rocks back as soon as 2031.

The Trump administration, meanwhile, has signaled through its budget proposal that it wants to cancel a planned Mars Sample Return mission, a joint project with the European Space Agency.

It has hinted the job could instead be accomplished by a crewed mission, although no firm details have been provided.