Two objects spotted in the southern Indian Ocean may be debris from the missing Malaysia Airlines Flight 370, Australian authorities said Thursday, fueling hopes of a breakthrough in an international search of unprecedented scale.

The objects are indistinct but of "reasonable size," with the largest about 24 meters (79 feet) across, said John Young, general manager of emergency response for the Australian Maritime Safety Authority.

They appear to be "awash with water and bobbing up and down" in an area 2,500 kilometers (1,500 miles) southwest of Australia's west coast, he said.

"If that piece of the plane is that big, maybe it's the tail section" said David Gallo, one of the leader of the search for Air France Flight 447, which crashed in the Atlantic Ocean in 2009. But he warned that the size gave him a degree of concern.

"It's a big piece of aircraft to have survived something like this," he said.

The tail height of a Boeing 777, the model of the missing Malaysian plane, is 60 feet.

The announcement raised the prospect of finding parts of the plane amid a huge search that is now in its 13th day. The plane vanished over Southeast Asia on March 8, and previous reports of debris found in the sea have turned out to be red herrings.

Australian Prime Minister Tony Abbott first announced the discovery to the House of Representatives in Canberra on Thursday. Australian search teams have been at the forefront of the hunt for the missing plane in the remote southern Indian Ocean.

"There have been so many false leads and so many starts and changes and then backtracking in the investigation," said Mary Schiavo, a CNN aviation analyst and former inspector general for the U.S. Department of Transportation. "He wouldn't have come forward and said if they weren't fairly certain."

But officials cautioned that there were no guarantees that the objects now being investigated would prove to be from the missing plane.

At the Lido Hotel in Beijing where family members of some of the passengers on the missing plane have waited for news for days, relatives gathered around a large screen television watching the Australian news conference. They leaned forward in their chairs, hanging on every word. Some sighed loudly.

Malaysia Airlines said it won't be sending representatives or family members to Australia unless the objects are confirmed as plane debris.

'The best lead we have right now'

The images of the objects were captured by satellite and were being assessed by the Australian Geospatial-Intelligence Organisation. The images were taken near the area of the southern Indian Ocean that has been scoured by search teams in recent days.

Although the total search area for the plane spans nearly 3 million square miles, a U.S. government official familiar with the investigation said the missing plane is most likely somewhere in the southern Indian Ocean.

"This is an area out of normal shipping lanes, out of any commercial flight patterns, with few fishing boats, and there are no islands," the official said.

Young cautioned that the images may not be from the plane. There can be other debris out there, like containers that have fallen overboard from ships, for example.

The objects were seen in the heart of what is known as the Indian Ocean Gyre. There is little to no oceanic current movement in the region and the area is notorious for trapping debris. It's one of the five major gyres in the world's oceans and is known to contain a "garbage patch."

"It is probably the best lead we have right now," Young said. "But we need to get there, find them, see them, assess them to know whether it's really meaningful or not."

The visibility in the area is poor, Young warned. "The weather is not playing the game with us," he said.

Planes arrive

A Royal Australian Air Force Orion aircraft has already arrived in the area, Young said, and three other planes are being sent there, including a New Zealand Air Force Orion and U.S. Navy P8 Poseidon.

The flight crew on the Poseidon say they're getting radar hits of "significant size," indicating something lying below the water's surface, ABC News reported Thursday.

ABC's correspondent David Wright, who is on board the aircraft, says the crew told him that the radar indicates that "there is something down there." But ABC cautioned that it is still too early to tell if the radar hits are related to the missing plane.

An Australian C-130 Hercules plane has been tasked by Australian authorities to drop marker buoys in the area, Young said.

"The first thing they need to do is put eyes on the debris from one of the aircraft," said aviation expert Bill Waddock. The buoys will mark the place and transmit location data.

A merchant ship helping Australian authorities in the search was also expected to arrive in the area Thursday.

'Every lead is a hope'

The Malaysian Navy has six navy ships with three helicopters heading to the southern Indian Ocean to take part in the search, a Malaysian government source said.

"Verification might take some time. It is very far and it will take some time to locate and verify the objects," the Malaysian government source said.

See updates on this story at CNN.com.