ABC News reported that a US Navy P-8 Poseidon was involved in the search, occurring about 1,500 miles off of Australia's coast.
According to ABC, about 6 hours after the objects were spotted, the P-8 and one other plane returned without having identified anything connected with the missing flight. Rain and cloudy weather were said to be hampering search efforts.
The other two planes and the merchant ship continued searching for the two objects.
One of the objects spotted by satellite imagery had a dimension of 24 meters (almost 80 feet) in length and the other one 5 meters (15 feet). There could be other objects in waters nearby in the area that's a four-hour flight from Australia's southwestern coast, said John Young, manager of Australian Maritime Safety Authority's emergency response division.
"This is a lead, it's probably the best lead we have right now," Young said. He cautioned that the objects could be seaborne debris along a shipping route where containers can fall off cargo vessels, although the larger object is longer than a container.
Young told a news conference in Canberra, Australia's capital, that planes had been sent to the area about 2,500 kilometers (1,550 miles) southwest of Perth to check on the objects. He said that satellite images "do not always turn out to be related to the search even if they look good, so we will hold our views on that until they are sighted close-up."
Australian Prime Minister Tony Abbott had earlier told Parliament about the debris, and said Orion search aircraft had been dispatched.
Young said visibility was poor and may hamper efforts to find the objects. He said they "are relatively indistinct on the imagery ... but those who are experts indicate they are credible sightings. The indication to me is of objects that are a reasonable size and probably awash with water, moving up and down over the surface."
Military planes from Australia, the U.S. and New Zealand have been covering a search region over the southern Indian Ocean that was narrowed down from 600,000 square kilometers (232,000 square miles) to 305,000 square kilometers (117,000 square miles).
Young said the depth of the ocean in the latest area, which is south from where the search had been focused on since Monday, is several thousand meters (yards). He said commercial satellites had been redirected in the hope of getting higher resolution images. He did not say when that would happen. The current images are not sharp enough to determine any markings.
The Australian Maritime Safety Authority released two images of the whitish objects floating on or just under the surface. The images were taken March 16, but Australian Air Commodore John McGarry said it takes time to analyze.
"The task of analyzing imagery is quite difficult, it requires drawing down frames and going through frame by frame. The moment this imagery was discovered to reveal a possible object that might indicate a debris field, we have passed the information from defense across to AMSA for their action," he told the news conference.
The hunt for the Boeing 777 has been punctuated by several false leads since it disappeared March 8 above the Gulf of Thailand.
Oil slicks that were spotted did not contain jet fuel. A yellow object thought to be from the plane turned out to be a piece of sea trash. Chinese satellite images showed possible plane debris, but nothing was found.
Relatives of passengers, who have been huddled at a Beijing hotel awaiting news, said Thursday they did not want to comment until there was more solid information out of Australia.
But this is the first time that possible objects have been spotted since the search area was massively expanded into two corridors, one stretching from northern Thailand into Central Asia and the other from the Strait of Malacca down to southern reaches of the Indian Ocean.
Abbott said he spoke to the prime minister of Malaysia, Najib Razak, about the latest developments.
The FBI has also joined forces with Malaysian authorities in analyzing deleted data on a flight simulator belonging to the pilot of the missing jet.
Files containing records of flight simulations were deleted Feb. 3 from the device found in the home of the pilot, Capt. Zaharie Ahmad Shah, Malaysian police chief Khalid Abu said.
It was not clear whether investigators thought that deleting the files was unusual. They might hold hints of unusual flight paths that could help explain where the missing plane went, or the files could have been deleted simply to clear memory for other material.
Malaysian Defense Minister Hishammuddin Hussein told a news conference Wednesday that Zaharie is considered innocent until proven guilty. He said members of the pilot's family are cooperating in the investigation.
Zaharie was known to some within the online world of flight simulation enthusiasts.
A U.S. official, speaking on condition of anonymity because the official was not authorized to discuss the ongoing investigation by name, said the FBI has been asked to analyze the deleted simulator files.
U.S. Attorney General Eric Holder said in Washington that the FBI was working with Malaysian authorities. "At this point, I don't think we have any theories," he said.
Flight 370 disappeared March 8 on a night flight from Kuala Lumpur to Beijing. Malaysian authorities have not ruled out any possible explanation, but have said the evidence so far suggests the flight was deliberately turned back across Malaysia to the Strait of Malacca, with its communications systems disabled. They are unsure what happened next.
Investigators have identified two giant arcs of territory spanning the possible positions of the plane about 7½ hours after takeoff, based on its last faint signal to a satellite - an hourly "handshake" signal that continues even when communications are switched off. The arcs stretch up as far as Kazakhstan in central Asia and down deep into the southern Indian Ocean.
Police are considering the possibility of hijacking, sabotage, terrorism or issues related to the mental health of the pilots or anyone else on board, and have asked for background checks from abroad on all foreign passengers.
Gelineau reported from Sydney, Australia. Associated Press writer Rod McGuirk in Kuala Lumpur contributed to this report.