No time limit on Malaysia jet search: Australian Prime Minister Tony Abbott

Australian Prime Minister Tony Abbott said there was no time limit on the hunt for Malaysia Airlines Flight MH370 , missing for more than three weeks in the Indian Ocean with 239 people on board.

A total of 20 aircraft and ships will resume scouring a massive area in the Indian Ocean some 2,000 km (1,200 miles) west of Perth on Monday, search authorities said.

"I'm certainly not putting a time limit on it," Abbott told reporters after meeting flight crews at Pearce airbase in Perth.

"The intensity of our search and the magnitude of operations is increasing, not decreasing," he said, adding that searchers owed it to grieving families of passengers to continue the hunt.

Families have strongly criticised Malaysia's handling of the search and investigation, including the decision last week to say that, based on satellite evidence, the plane had crashed in the southern Indian Ocean.

Abbott rejected suggestions his Malaysian counterpart had been too hasty to break that news, given that no confirmed wreckage from the plane has been found and its last sighting on radar was northwest of Malaysia heading towards India.

"No, the accumulation of evidence is that the aircraft has been lost and it has been lost somewhere in the south of the Indian Ocean," he said.

Malaysia says the plane, which disappeared less than an hour into a flight from Kuala Lumpur to Beijing, was likely diverted deliberately far off course. Investigators have determined no apparent motive or other red flags among the 227 passengers or the 12 crew.

China has also been critical in Malaysia's handling of the case, but in a sign of softening, the official China Daily said it was understandable that not all sensitive information could be made public.

"Although the Malaysian government's handling of the crisis has been quite clumsy, we need to understand that this is perhaps the most bizarre incident in Asia civil aviation history," the editorial on Monday read.

"Public opinion should not blame the Malaysian authorities for deliberately covering up information in the absence of hard evidence."

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Dozens of items have been spotted since Australian authorities moved the search 1,100 km (685 miles) north after new analysis of radar and satellite data, but none has been linked to Flight MH370.

A multinational air search team and 10 ships, including seven Chinese vessels, two Australian navy craft and a merchant ship were searching the area on Monday, the Australian Maritime Safety Authority said in a statement.

The new search area, while closer to Perth and subject to calmer weather, is also closer to an area of the Indian Ocean where currents drag all manner of flotsam and rubbish.

"I would say the search area is located just outside of what we call the garbage patches," Erik van Sebille, an oceanographer at the University of New South Wales said.

"However, there is much more debris there than in the Southern Ocean. Debris from Western Australia that ends up in the garbage patches will have to move through the search area."

However the greatest problem remains the vast search area, roughly the size of Poland or New Mexico.

"If you compare this to Air France flight 447, we had much better positional information of where that aircraft went into the water," U.S. Navy Captain Mark Matthews said on Sunday , referring to a plane that crashed in 2009 near Brazil and which took more than two years to find.

Among the vessels due to join the search in the coming days is an Australian defence force ship, the Ocean Shield, that has been fitted with a sophisticated U.S. black box locator and an underwater drone.

However, they cannot be used until "conclusive visual evidence" of debris is found, U.S. Navy spokesman Commander William Marks told CBS's "Face the Nation" programme.

If no location is found, searchers would have to use sonar to slowly and methodically map the bottom of the ocean, he said. "That is an incredibly long process to go through. It is possible, but it could take quite a while," he said.