"Two Chinese Sukhoi Su-30 jets have conducted an "unprofessional" intercept of a US aircraft, the US military said.
One of the Chinese jets came as close as 150ft (45m) to the US WC-135 plane and flew upside down above it, according to US officials cited by CNN.
The US says the plane was on a mission to detect radiation in international airspace over the East China Sea.
Tensions have repeatedly risen over US activity near the resource-rich international waters off China's coast.
The intercept, which took place on Wednesday, was deemed unprofessional "due to the manoeuvres by the Chinese pilot, as well as the speeds and proximity of both aircraft," Air Force spokesman Lt Col Lori Hodge said.
He said the issue was "being addressed with China through appropriate diplomatic and military channels", and a military investigation was under way."
We were in International Airspace, and on a mission. I think they were out of line, and ..um.. kinda showing off flying upside down. Odd. :O