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Eight people have been found alive and are in "good condition" after a U.S. Navy plane with 11 people aboard crashed into the sea off Japan on Wednesday, the military said.

A search-and-rescue mission for three other people continues, the Navy said.

"Our entire focus is on finding all of our sailors," Rear Adm. Marc H. Dalton said in a statement, adding that the Navy "will be relentless in our efforts."

The aircraft is believed to have crashed about 500 nautical miles southeast of Okinawa Island at about 2:45 p.m. (12:45 a.m. ET) while on the way to the USS Ronald Reagan aircraft carrier.

Eight of the 11 Navy personnel were rescued 45 minutes later before being transferred to the ship for medical evaluation. The aircraft carrier, which is in the Philippine Sea, is part of the Japan-based 7th Fleet.

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Search-and-rescue efforts were being conducted by ships and aircraft of the U.S. Navy and the Japan Maritime Self-Defense Force. Families of the three missing people were officially informed that they were listed as "duty status whereabouts unknown," but their names were being withheld for 72 hours under Navy policy, the Navy said.

"The Japanese navy is helping us with many, many assets, but we should keep our fellow Navy family people in our thoughts and prayers," Navy Secretary Richard Spencer said Wednesday during a visit to Naval Support Activity Bahrain, home to U.S. Naval Forces Central Command and the U.S. 5th Fleet.

The aircraft was taking part in a U.S.-Japan naval exercise off the coast of Okinawa in which 14,000 U.S. personnel were participating.

The annual exercise is "designed to increase the defensive readiness and interoperability of Japanese and American forces through training in air and sea operations," a statement on the event said earlier this month.

The @USNavy is conducting search and rescue following aircraft crash. We are monitoring the situation. Prayers for all involved. https://t.co/1AxmegKqvu — Donald J. Trump (@realDonaldTrump) November 22, 2017

The plane was conducting a routine transport flight carrying passengers and cargo from Marine Corps Air Station Iwakuni to the USS Ronald Reagan at the time of the crash, according to the Navy.

The aircraft's role included the transport of high-priority cargo, mail, duty passengers and distinguished visitors between the USS Ronald Reagan and shore bases throughout the Western Pacific and Southeast Asia, the statement added.

The Navy said the incident would be investigated.

The crash comes at a time when the Navy's 7th fleet and U.S. Pacific Command have come under increased scrutiny after 17 sailors died in two deadly collisions in Asian waters this year.

A C-2A Greyhound like this one went down in the sea off Japan. Stocktrek Images / Getty Images file

Seven U.S. sailors died when the USS Fitzgerald collided with a container ship off the coast of Japan in June. Two months later, in August, another navy destroyer, the USS John S. McCain, collided with an oil tanker near Singapore, killing 10 sailors.

In the wake of the accidents, eight top Navy officials were removed from their posts, including the 7th Fleet commander. After the second collision, the Navy ordered the entire fleet to take a one-day "operational pause" to ensure that the ships were meeting safety standards.

The Navy said a family assistance center had been set up. Families living on base in Japan can call 315-243-1728, while families living in the United States can call +81-468-16-1728.