Satellites have joined the search for missing Malaysia Airlines flight MH370, joining 42 ships and 39 aircraft deployed in an "unprecedented" search for the missing airliner.

The move came after China requested activation of the so-called International Charter on Space and Major Disasters, an agreement under which 15 space agencies or institutes can help emergency or relief efforts by passing on satellite images, according to a report from AFP.

"Satellite imagery is now being employed to search for any evidence of the plane, both before and after it disappeared," the charter's website said.

Flight MH370 took off from Kuala Lumpur for Beijing early on Saturday morning and last made contact with ground control officials about 35,000 feet (10,600km) above the Gulf of Thailand, between Malaysia and southern Vietnam before vanishing.

Hishammuddin Hussein, Malaysia's transport minister, on Wednesday said the sea and air search for the missing plane had been expanded to two areas and now covered almost 50,000 square kilometres.

Hussein described the search effort for the missing plane with 239 people on board as "unprecedented" and said authorities would continue searching until they found it. The operation is a multinational effort with 12 countries now taking part.

Hussein gave his assurance to the families of passengers and crew that no efforts would be spared in finding the plane.

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"We will never give up hope," he said.

Rodzali Daud, the head of the Royal Malaysian Air Force (RMAF), said radar detected what could have been the jetliner in an area in the northern Malacca Strait, hundreds of kilometres from the spot where the plane dropped off air traffic screens.

Daud told the joint news conference that an aircraft was tracked at 2:15am local time on Saturday, about 45 minutes after the plane with 239 people on board vanished from air traffic control screens midway between Malaysia's east coast and Vietnam.

He said the aircraft was at a point 320km northwest of Penang island on Malaysia's west coast. 

Flight path confusion

Earlier, there were reports that he had denied saying the airliner had turned back towards Kuala Lumpur, flying hundreds of kilometres to the west.

Malaysia's Berita Harian newspaper had quoted General Tan Sri Rodzali Daud as saying military radar detected the plane near the island of Pulau Perak, at the northern end of the Strait of Malacca, flying about 1,000 metres lower than its previous altitude.

However, Daud said the RMAF had not ruled out the possibility the aircraft had turned back before vanishing from the radar.

On Monday, Malaysian authorities doubled the search radius to 185km around the point where Malaysia Airlines MH370 disappeared from radar over the South China Sea.

"The biggest problem is just knowing where to look, especially at night," Vo Van Tuan, a top Vietnamese military officer who is leading Vietnam's search effort, told the AFP news agency.

The total search sphere now includes land on the Malaysian peninsula itself, the waters off its west coast, and an area to the north of the Indonesian island of Sumatra.

Police had earlier said they were investigating whether any passengers or crew on the plane had personal or psychological problems that might explain its disappearance, along with the possibility of a hijack.

On Tuesday, Interpol said the disappearance of the plane was not likely to have been caused by a "terrorist" attack.

"The more information we get, the more we are inclined to conclude it was not a terrorist incident," Ronald Noble, head of Interpol said.

Source: Al Jazeera and agencies