The 13-day search for Malaysia Airlines flight 370 could be close to resolution after satellite images picked up what appears to be a 24-metre long bobbing object in waters off the Australian coast.
Imagery released by the Department of Defence showing the largest piece of potential wreckage.
But the Australian Maritime Safety Authority said efforts by aircraft to locate the objects were being hampered by poor visibility and weather on scene.
The possible breakthrough, revealed by Prime Minister Tony Abbott in Parliament on Thursday afternoon, could bring resolution for the families of the 239 missing passengers following a massive international land and sea search involving dozens of countries.
The maritime authority said on Thursday it had not been able to confirm if the objects located by satellite 2500 kilometres south-west of Perth were debris from the missing plane.
ASMA has released satelite images of the unidentified objects.
The objects in the satellite images, which were released on Thursday evening, were described by the authority as "indistinct" but the sightings had been assessed and were credible.
John Young from AMSA's emergency response division said the objects were of a reasonable size and "probably awash with water bobbing up and down under the surface".
He said the largest object had been assessed as measuring 24 metres, with "another one that's smaller than that" and a number of other images located in the vicinity of the largest object.
Prime Minister Tony Abbott announces that satellite images show objects in the waters off Perth that could be debris from the missing Malaysian Airlines flight. Photo: Andrew Meares
"We have to get there, find them, see them, assess them," he said, to confirm if the images were debris from the missing plane.
"The weather is not playing the game with us. We may get a sighting, we may not."
US television network ABC has reported that US naval craft dispatched to the site had picked up significant "radar returns" from the search area.
Australian Maritime Safety Authority's John Young addresses the media on the latest in the search for a press missing Malaysia Airlines flight MH370. Photo: Andrew Meares
"Crew on @USNavy P-8 spotter tell [of] ‘significant radar returns’ coming from site where possible MH370 objects spotted," ABC foreign editor Jon Williams tweeted.
Mr Young said water in the search area would be several thousand metres deep.
"This is a lead, it's probably the best lead we have right now, but we need to get there, find them, see them, assess them to know whether it's really meaningful or not and I caution again they will be difficult to find."
Debris found in search for MH370
Missing Malaysia Airlines plane: Debris found in search for MH370, says Australian Prime Minister Tony Abbott. Photo: Supplied
Search aircraft at scene
Mr Young said the images were close enough to the National Transportation Safety Board's assessment area to potentially be linked to the 777.
He said the first royal Australian Airforce Orion aircraft had arrived in the search area at 1.50 pm on Wednesday.
Family members of missing Malaysia Airlines flight MH370 pray for their loved ones at a prayer room at the Lido Hotel in Beijing. Photo: Sanghee Liu
A further three aircraft have been tasked to the area.
A Poseidon from the US was also on scene, while a New Zealand Orion was due to arrive at 8pm.
A second Australian Orion is due to arrive at 6pm.
A P-3 Orion aircraft.
Mr Young said an Australian Hercules had been tasked to drop marker buoys to mark the search base.
Australia took charge of the search for the missing plane in the Indian Ocean on Monday.
The Indian Ocean lies on one of two "vectors" that authorities identified on the weekend as paths the mystery flight might have taken.
The Australian-led search, supported by the US and New Zealand, began in a massive stretch of ocean west of Perth.
News of the potential breakthrough emerged on Thursday afternoon when Mr Abbott told Parliament that an Australian P-3 Orion aircraft had been diverted to check out the objects and would be followed by other planes.
But Mr Abbott described the breakthrough as "new and credible information".
"The Australian maritime safety authority has received information based on satellite imagery of objects possibly related to the search," Mr Abbott said.
"Following specialist analysis of this satellite imagery, two possible objects related to the search have been identified."
"I should tell the House - and we must keep this in mind - the task of locating these objects will be extremely difficult and it may turn out that they are not related to the search for flight MH370," Mr Abbott said.
"Nevertheless, I did want to update the House on this potentially important development.’’
Mr Abbott said he had informed his Malaysian counterpart, Prime Minister Najib Razak, and promised to keep him updated.
Families wait in hope
Malaysia's acting transport minister Hishammuddin Hussein urged caution about the news but said ''with every lead there is hope".
"We will need to wait for the aircrafts to go to the area," he said.
"We need to verify."
Malaysians gathered around televisions in cafes and hotel lobbies to watch the press conference.
Malaysian Insider website flashed "the best lead we have had until now".
Acting transport minister Hissammuddin was locked in briefings at the search headquarters in the Sama Sama Hotel near Kuala Lumpur airport.
Mr Hishammuddin said he had not being told what kind of debris had been sighted.
Earlier a senior Australian navy officer left search headquarters at a Kuala Lumpur hotel.
"I can't comment," he said.
Prime minister Najib Razak received a call from Mr Abbott informing him that "two possible objects had been identified the southern Indian Ocean," Mr Hishammuddin said.
The Australian High Commission in Kuala Lumpur had also briefed him on the situation.
"At this stage, Australian officials have yet to establish whether these objects are indeed related to the search for MH370," Mr Hishammuddin said.
At the Lido Hotel in Beijing, where families have waited desperately for information on their loved ones, grim-faced relatives filed into a hotel conference room to watch a live broadcast of the Australian press conference.
About 100 people in the room watched silently and intently, with police and medical personnel standing by at the back.
A sad, collective sigh went up in the room when the Australian official said the first thing to do would be to check for survivors.
One woman in a blue jumper, who said her husband was on the Malaysia Airlines flight, told Fairfax Media through tears that she hoped the Australian government was wrong and that the objects would not prove to be wreckage of the plane.
"I hope it's not the truth," she said.
With Lindsay Murdoch, Philip Wen