Searchers Saturday scoured a new area of the Indian Ocean for a Malaysian passenger jet which went missing three weeks ago, hoping finally to find debris from the plane after several possible sightings.

China, which lost 153 people when the Boeing 777 went down, was at the forefront of the sweep across a vast ocean expanse about the size of Norway.

One of its ships -- the Haixun 01 -- began hunting at first light for multiple unidentified objects seen from the air the previous day. And a Chinese air force Ilyushin IL-76 was the first of eight aircraft to depart an air base near the west Australian city of Perth.

China's state news agency said the plane crew had spotted three unidentified floating objects coloured white, red and orange. The Haixun 01 would try to trace and retrieve them.

Numerous satellite and air sightings of unidentified debris have raised hopes that wreckage of the Malaysia Airlines plane will soon be found.

Malaysia has announced that the plane must have been lost at sea with the loss of all 239 aboard.

But after three weeks of false leads and sometimes conflicting information, many desperate and angry relatives are refusing to abandon hope till physical proof of a crash is found.

"Everyone knows that you are concealing the truth and delayed the research!" one of them told Malaysian officials at a tense briefing in Beijing on latest developments.

The search moved Friday to a new sea zone after fresh data indicated the plane was flying faster than first thought before it plunged into the sea on March 8.

That disappearance, during a flight from Kuala Lumpur to Beijing, is one of the biggest mysteries in aviation history.

Malaysia believes the plane was deliberately redirected by someone on board and flown thousands of miles southwards, but nothing else is known.

Attention has focused on the pilot but Malaysian transport minister Hishammuddin Hussein said nothing incriminating had been found on a flight simulator seized at his home.

Australian Prime Minister Tony Abbott -- whose country is coordinating the search -- said teams faced a formidable task.

"We should not underestimate the difficulty of this work, it is an extraordinarily remote location," he told reporters.

"We are trying to find small bits of wreckage in a vast ocean. While we're throwing everything we have at it, the task goes on."

The Australian Maritime Safety Authority (AMSA) said a total of six ships -- five of them Chinese -- were expected to be in place in the search area 1,850 kilometres (1,160 miles) west of Perth by the end of Saturday, along with eight planes from four countries.

Yet the objects they are trying to find are tiny, with New Zealand Air Vice-Marshal Kevin Short saying the items spotted from a New Zealand Orion Friday were mostly rectangular and ranging in size from just 50 to 100 centimetres (20 to 40 inches).

The search sector "was shifted north after international air crash investigators in Malaysia updated their previous analysis of the likely aircraft movements", AMSA said.

The new zone is closer to land, meaning planes can spend more time searching before having to return to refuel, and enjoys better weather than seas further south where the search had been concentrated.

Adding to the urgency is the time limit on the tracking signal emitted by the plane's "black box" of flight data. It lasts about 30 days.

The US Pacific Fleet has moved specialised black box locator equipment to Perth and Abbott said it would be deployed on an Australian navy ship once an approximate crash site is established.

Chinese media, officials and relatives have all criticised what they see as an inadequate and sometimes secretive response by Malaysia to the crisis.

Relatives have heaped abuse on Malaysian officials at briefings in Beijing.

On Saturday one woman responded angrily to information on aerial sightings of debris.

"Thanks for this technical rubbish, but we are not technical people here, we want straight and plain answers!" she said.

"With so much debris, how do you explain that no piece at all has been retrieved yet?"

Malaysia also came under fire from Interpol, which rejected its claims that consulting a stolen passport database -- which may have detected two people using false passports on the flight -- would have caused excessive delays.

The pair are thought to have been Iranian asylum-seekers with no known terror links

While Kuala Lumpur's handling of the mysterious disappearance has been criticised by some families, Abbott said international protocols meant Malaysia would remain in charge of the operation.

"The prime responsibility rests with Malaysia (but) Australia is ready to shoulder as much of the responsibility as countries wish us to take," he said.