China's test of an earth-circling hypersonic missile has been compared to the Soviet Union's launch of the world's first satellite, Sputnik, in 1957, which resulted in the countries' space race.
“What we saw was a very significant event of a test of a hypersonic weapon system. And it is very concerning,” Mr Milley told Bloomberg TV.
“I don't know if it's quite a Sputnik moment, but I think it's very close to that,” he said. “It's a very significant technological event that occurred … and it has all of our attention.”
The US Department of Defence previously declined to confirm the test, first reported by the Financial Times on October 16. The newspaper said the August test launch caught Washington by surprise. The missile circled the Earth at a low altitude and a velocity of more than five times the speed of sound, although it missed its target by more than 30 kilometres, the Financial Times said.
China denied the report, saying it was a routine test of a reusable space vehicle.
Hypersonics are the new frontier in missile technology because they fly lower and are therefore harder to detect than ballistic missiles, can reach targets more quickly, and are manoeuvrable. That makes them more dangerous, particularly if mounted with nuclear warheads.
Which countries are testing hypersonics?
China in 2019 unveiled a hypersonic medium-range missile, the DF-17, which can travel around 2,000 kilometres and carry nuclear warheads. The missile mentioned in the Financial Times story is a different one, with a longer range. It can be launched into orbit before coming back into the atmosphere to hit its target.
Pentagon spokesman John Kirby declined to confirm China's test when asked about it on Wednesday. But he said any major advancement in China's military capabilities does “very little to help decrease tensions in the region and beyond.”
Such advances, he said, are “paired with a foreign and defence policy approach that uses intimidation and coercion of neighbouring nations to yield to China's interests”.