Honolulu: Rescue crews were scouring a vast area covered with floating debris and a sheen of oil on Monday for crew members of a US Air Force B-52 bomber that crashed off the island of Guam, officials said.

At least two people were recovered from the waters, but their condition was not immediately known, the US Coast Guard said.

Six vessels, three helicopters, two F-15 fighter jets and a B-52 bomber were involved in the search, which had covered about 180 square kilometres of ocean, said Coast Guard spokeswoman Lieutenant Elizabeth Buendia.

"We have an active search that's going to go on throughout the night," she said on Monday.

The Navy, Coast Guard, Air Force and local fire and police departments were involved in the efforts.

Second accident this year

The B-52 bomber based at Barksdale Air Force Base in Louisiana was en route to a Liberation Day parade when it crashed around about 50 kilometres northwest of Apra Harbour, the air force said.

The parade marks the day when the US military arrived on Guam to retake control of the island from Japan.

The air force said a board of officers will investigate the accident.

The accident is the second for the air force this year on Guam, a US territory 5,950 kilometres 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 (Dh5.1 billion). The B-52 is a long-range, heavy bomber that can refuel in mid air.

Since the 50-metre-long bomber was first placed into service in 1955, it has been used for a wide range of missions from attacks to ocean surveillance. Two B-52s, in two hours, can monitor 360,000 square kilometres of ocean surface.

According to the air force's website, the B-52 Stratofortress has been the backbone of the manned strategic bomber force for the US for more than four decades.

It is capable of dropping or launching the widest array of weapons in the US inventory.