Aircraft from New Zealand and the United States will bolster Australian search efforts in the southern Indian Ocean on Wednesday as the operation to find Malaysia Airlines flight MH370 continues.

Four RAAF aircraft have already started sweeping a 600,000 square kilometre patch of ocean some 3200 kilometres southwest of Perth, calculated as a possible location for the jet, which went missing with 239 people on board.

“A further three Air Force P-3 Orions will join the search,” John Young, head of the Australian Maritime Safety Authority’s emergency response division, said of plans for Wednesday.

A New Zealand Air Force P-3 Orion will also head to the search zone on Wednesday, along with a US Navy P-8 Poseidon aircraft.

China has offered more assistance.

Australia is co-ordinating the effort in that region because the search zone falls into its international maritime responsibility.

The search of the area has been described as difficult and is expected to take weeks.