The Japan Coast Guard says an air ambulance may have ditched in waters off Nagasaki Prefecture, western Japan, as no major damage to the aircraft has been detected.



The helicopter is said to have lost contact with controllers about 10 minutes after leaving an airport on Tsushima Island for a hospital in Fukuoka Prefecture on Sunday. It was later found floating upside down.



The Coast Guard officials say three of the six people who were on board -- an 86-year-old patient, her son and a doctor -- have been confirmed dead. They say the other three -- a pilot, a mechanic and a nurse -- are alive and conscious.



The officials say investigators have found no major damage to the chopper's rotors so far.



The Coast Guard plans to speak with the pilot to find out how the incident occurred.



The Transport Safety Board is scheduled to launch an on-site investigation on Monday.