China said one of its fighters crashed today after being rammed in mid-air by a US aircraft, which landed on the southern island of Hainan without permission.
A Foreign Ministry statement said China had made a solemn representation and protest over the incident and reserved the right to seek damages.
According to the US Navy version of the incident, one of its EP-3 Marine patrol aircraft was on a routine surveillance mission over the South China Sea when it brushed one of two Chinese fighters on an interception mission.
The four-engine propeller plane carrying 24 crew made an emergency landing on Hainan, the US statement said.
But China laid the blame squarely on the US plane.
"A Chinese aircraft was conducting normal flight operations 104 km (60 miles) south of Hainan island when a US plane suddenly veered towards it," Chinese state television quoted the Foreign Ministry statement as saying.
"The nose and left wing of the US plane hit the Chinese plane and caused it to crash," the statement said."China is now searching for the crew," it added.
The Chinese statement also threatened further representations over the US plane entering Chinese air space and landing without permission.
"China was making proper arrangements for the 24 crew," the statement added, without giving any details.
The US government said it expected China to return the crew.
"That is our expectation. That is the standard practice. We would expect them to follow it," White House spokesman Ari Fleischer said.
A US statement called on China to respect the integrity of the aircraft and the well-being and safety of the crew in accordance with international practices, expedite any necessary repairs to the aircraft and facilitate the immediate return of the aircraft.
"There was contact between one of the Chinese aircraft and the EP-3, causing sufficient damage for the U.S. plane to issue a 'mayday' signal and divert to an airfield on Hainan Island," the US statement said.
It added that the US had communicated our concerns to the Chinese government.
It was not immediately known whether the US plane was in international air space at the time. Japan's Kyodo news agency said it was based in Kadena Air Base in Okinawa.
A US Navy spokeswoman said the plane was believed to be carrying one member of the Air Force, one Marine, and 22 Navy personnel.
"There were no injuries that we know of related to the landing, they landed safely. But we have not received any communication since the landing," she said.