Moscow and Beijing have invested heavily in new aircraft and a senior Pentagon chief admitted the country's newest jets were "much faster" than expected.
The great leap forward has worried American officials enough to make them reconsider their fighter jet programme, which is key to defeating Islamic State (ISIS) in the Middle East.
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Lieutenant General James Holmes, a US Air Force deputy chief of staff, said: "We've seen both Russia and China develop airplanes much faster than was anticipated.
"Congress made a decision that we would not see a near-peer threat within a number of years, and that decision, that judgment also proved to be optimistic."
Russia's main strike force comprises of the Sukhoi Su-34 and Su-35S supermaneuverable multirole fighters.
China relies on a number of domestically manufactured jets, including the J-15 Flying Shark.
But the Asian powerhouse has the world's biggest army with more than two million recruits in active service.