Media playback is unsupported on your device Media caption Acting Malaysian Transport Minister Hishammuddin Hussein said families were "heartbroken"

Rescue crews have put no time limit on the search for the missing Malaysia Airlines plane, Australian Prime Minister Tony Abbott has said.

Mr Abbott told reporters near Perth, where the operation is being co-ordinated, that the hunt for flight MH370 was still being stepped up.

Ten aircraft and 11 ships are scouring the sea west of Perth for debris from the airliner.

The Beijing-bound plane disappeared on 8 March with 239 people on board.

The search teams are deploying a device known as a "towed pinger locator" (TPL) to listen for ultrasonic 'pings' from the plane's "black box" flight-data recorders.

The signals from the flight recorders last about 30 days.

Media playback is unsupported on your device Media caption The BBC's Jon Donnison explains how a "towed pinger locator" is used

Several floating objects have been found in recent days, but none is believed to belong to the missing plane.

"We can keep searching for quite some time to come," said Mr Abbott.

"The intensity of our search and the magnitude of our search is increasing, not decreasing."

On Monday, Malaysian acting Transport Minister Hishammuddin Hussein said the search area was 254,000 sq km (98,000 sq miles), according to the Australian authorities.

The search involved nine military aircraft and one civilian, as well as eight Chinese and three Australian ships.

The Australian naval support vessel, ADV Ocean Shield, fitted with the TPL, is expected to arrive in the area on 3 April, he added.

'Heartbroken'

Some 153 of the passengers were Chinese, and dozens of their relatives arrived in Kuala Lumpur on Sunday.

They have become increasingly angry with the perceived lack of information from the Malaysian authorities.

Media playback is unsupported on your device Media caption Nick Hardman-Mountford explains how ocean currents can move debris along

On Monday, Mr Hussein said the government would soon hold a briefing for those families to update them on the search for MH370, which would include international experts to explain the research, data and methodology used in the operation.

The briefing would also be broadcast live to other families in Beijing, he said.

Of his encounter with the families, Mr Hussein said it was "the most difficult meeting" he had ever attended.

"The families are heartbroken. For many, the strain of the past few weeks has been unbearable," he said, adding Malaysia would not "give up hope. We will continue with all our efforts to find MH370".

MH370 - Facts at a glance 8 March: Malaysia Airlines Kuala Lumpur-Beijing flight carrying 239 people disappears

Malaysia Airlines Kuala Lumpur-Beijing flight carrying 239 people disappears Plane's transponder, which communicates with ground radar, was switched off as it left Malaysian airspace

Satellite 'pings' indicate plane was still flying seven hours after satellite contact was lost

24 March: Based on new calculations, Malaysian PM says "beyond reasonable doubt" that plane crashed in southern Indian Ocean with no survivors What we know The search for flight MH370

On Sunday, the families - chanting "tell us the truth" - said they wanted Malaysian Prime Minister Najib Razak to apologise for what they regard as misleading statements.

Many were outraged when Mr Najib stated earlier that he believed the plane had come down in the Indian Ocean with no survivors.

But Mr Abbott gave his backing to that assessment, saying: "The accumulation of evidence is that the aircraft has been lost and it has been lost somewhere in the south of the Indian Ocean.

"That's the absolutely overwhelming wave of evidence and I think that Prime Minister Najib Razak was perfectly entitled to come to that conclusion."

Various theories about what went wrong have been suggested - including the captain hijacking his own plane.

The speculation was fuelled by reports that files had been deleted on the pilot's home flight simulator.

However, on Saturday Mr Hussein said investigators had found "nothing sinister" from the simulator.

Malaysia Airlines Boeing 777 vanished less than an hour after taking off from Kuala Lumpur.

The airliner diverted off course and lost contact with air traffic controllers between Malaysian and Vietnamese air-traffic control areas.