The carrier USS Ronald Reagan is assisting in a search and rescue effort in the Pacific Ocean after a U.S. Navy plane with 11 on board crashed en route to the ship.

Japan is also assisting in the rescue on Wednesday and said it recovered eight from the wreckage of the C-2 “Greyhound” aircraft, but did not specify their conditions, reports Fox News.

“Personnel recovery is underway and their condition will be evaluated by USS Ronald Reagan medical staff,” US Navy 7th fleet said in a statement.

The plane, which was taking part in an ongoing joint U.S.-Japan naval exercise in waters surrounding Okinawa from Nov. 16-26, crashed into the Pacific about 150 kilometers (90 miles) northwest of Okinotorishima, a Japanese atoll, Defense Minister Itsunori Onodera said, according to a ministry spokesman.

The Navy called it the “premier training event” between the two navies, designed to increase defensive readiness and interoperability in air and sea operations.

The Navy said the ship was operating in the Philippine Sea when the crash occurred at 2:45 p.m. Japan time. The names of the crew and passengers are being withheld pending next of kin notification.

The cause of the crash was not immediately clear, however, Japanese Minister of Defence Itsunori Onodera told reporters that the U.S. Navy informed him that engine trouble might have caused the crash, reported Reuters.

The 7th Fleet was involved in two fatal accidents earlier this year in Asian waters that killed 17 sailors and led to the removal of eight top Navy officers from their posts, including the the 7th Fleet commander.