Two Chinese jets have carried out an "unprofessional" intercept of an American aircraft, according to the US military.
The Su-30 aircraft came within 150 feet of the US WC-135, with one of them flying upside down directly above it, CNN reported.
According to the US Pacific Air Forces, its aircraft was a radiation detection plane conducting duties in international airspace over the East China Sea. Air Force Lieutenant Colonel Hodge said:
"While we are still investigating the incident, initial reports from the US aircrew characterised the intercept as unprofessional."
"The issue is being addressed with China through appropriate diplomatic and military channels."
The US says it regularly uses its two WC-135s in Northeast Asia.
The aircraft, which have been used in the past to gather evidence of nuclear tests by North Korea, fly from Offutt Air Force Base in Nebraska.
China, however, accuses the US of carrying out reconnaissance missions over its waters and regularly calls for it to reduce patrols in the area.
It also claims sovereignty over almost all of the disputed territory in the South and East China seas, which it has backed with island-building and naval patrols.
However, several other countries in the region have competing claims.
The incident comes after the US reported an "unsafe" close encounter between a Navy plane and a Chinese surveillance aircraft over the South China Sea in February.
The American plane reportedly had to change course to miss the People's Liberation Army Air Force KJ-200 after coming within 1,000 feet.
These incidents are rare, with none taking place in 2015 and two in 2016.
Cover image a file photo of two Chinese SU-30s.