An Air Force B-52 bomber carrying six crew members and en route to conduct a flyover in a parade crashed off the island of Guam on Monday, officials said.
At least two people were recovered from the waters, but their condition was not immediately available, the Coast Guard said.
Rescue crews from the Navy, Coast Guard and local fire department launched a massive aerial and ocean search for the others in and around a vast area of floating debris and a sheen of oil.
The crashed occurred at 9:45 am on Monday about 48 kilometers northwest of Apra Harbor, the Air Force said.
The accident is the second for the Air Force this year on Guam, a US territory 6,000 kilometers southwest of Hawaii.
In February, a B-2 crashed at Andersen Air Force Base shortly after takeoff in the first-ever crash of a stealth bomber. Both pilots ejected safely. The military estimated the cost of the loss of the aircraft at $1.4 billion.
The latest mishap involved an aircraft from Barksdale Air Force Base in Louisiana as part of the Department of Defense's continuous bomber presence mission in the Pacific.
The B-52 was scheduled to fly over the Liberation Day parade, marking the day when Guam was liberated from Japan.
The Air Force said that a board of officers will investigate the accident.