NASA chief Bill Nelson said China could claim the moon as its own territory.
He told Politico that Chinese aggression in the South China Sea indicated what might happen on the moon.
Nelson said China had enjoyed "enormous success and advances" in its space program of late.
The head of NASA has said that China could claim the moon as its own territory if beats the US in the race to the lunar surface.
Nelson said: "It is a fact: we're in a space race. And it is true that we better watch out that they don't get to a place on the moon under the guise of scientific research. And it is not beyond the realm of possibility that they say, 'Keep out, we're here, this is our territory.'
"If you doubt that, look at what they did with the Spratly Islands."
Recently-published aerial photographs show new military installations on the Spratly Islands, a disputed archipelago in the South China Sea.
NASA completed its Artemis 1 mission in November, which involved flying an unmanned Orion spacecraft around the Moon. The mission preceded Artemis 3, which aims to land astronauts on the lunar surface by 2025.
China recently completed its new space station, Tiangong, and in November, launched a crew of taikonauts towards the station. Beijing plans to launch three missions to the moon over the next decade as part of its Chang'e lunar program, after saying it had discovered a new lunar mineral that could be used as an energy source.
Nelson told Politico that China has enjoyed "enormous success and advances" in its space program over the last decade.
NASA is working with Elon Musk's SpaceX on the Artemis 3 mission. Nelson told Politico: "I ask the question every day: 'How is SpaceX's progress?' And all of our managers are telling me they are meeting all of their milestones."
NASA didn't immediately respond to Insider's request for comment, made outside normal US operating hours.
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