By Michael Martina
PERTH (Reuters) - Australian Prime Minister Tony Abbott said on Monday the hunt for Malaysia Airlines Flight MH370 had no time limit, despite the failure of an international operation to find any sign of the plane in three weeks of fruitless searching.
A total of 20 aircraft and ships were again scouring a massive area in the Indian Ocean some 2,000 km (1,200 miles) west of Perth, where investigators believe the Boeing 777 carrying 239 people came down.
"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 our operations is increasing, not decreasing," he said, adding that searchers owed it to grieving families of passengers to continue the hunt.
Some families have strongly criticized 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 on March 8.
Abbott rejected suggestions his Malaysian counterpart, Najib Razak, 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.
Najib will travel to the western Australian city of Perth, the base for the search, on Wednesday to see the operations first hand, Malaysia's government 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."
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.
Several orange items recovered on Sunday turned out to be fishing equipment, a spokesman from the Australian Maritime Safety Authority (AMSA) said.
"Yesterday's finds were nothing of note, nothing related to the plane," he said.
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.
A Malaysian frigate arrived at HMAS Stirling naval base near Perth for briefings on the search area, AMSA added.
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."
But 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 defense force ship, the Ocean Shield, that has been fitted with a sophisticated U.S. black box locator and an underwater drone.
That equipment cannot be used until "conclusive visual evidence" of debris is found, U.S. Navy spokesman Commander William Marks told CBS's "Face the Nation" program.
If no location is found, searchers would have to use sonar to 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.
Time is running out because the signal transmitted by the black box will die about 30 days after a crash due to limited battery life, leaving investigators with a vastly more difficult task.
Malaysia's acting transport minister, Hishammuddin Hussein, said he would discuss the deployment of "more specific military assets" during a regional defense ministers' meeting with the United States in Hawaii that he is attending from Tuesday.
"I shall be discussing with the United States, and our other friends and allies, how best we can acquire the assets needed for possible deep sea search and recovery," said Hishammuddin, who is also Malaysia's defense minister.
(Additional reporting by Morag MacKinnon and Matt Siegel in Perth, Jane Wardell and Lincoln Feast in Sydney, Adam Jourdan in Shanghai and Andrea Shalal in Washington; Writing by Lincoln Feast; Editing by Alex Richardson)