Australian Maritime Safety Authority's rescue coordination center said the search area was expanded from 22,800 to 26,400 square miles on Monday, including a new separate area covered by data provided by France on Sunday.
Two Chinese Ilyushin IL-76 planes joined the search from Perth on Monday, increasing the number of aircraft from eight on Sunday to 10, AMSA said.
It said the weather in the search area, about 1,550 miles southwest of Perth, was expected to deteriorate with rain likely.
Australian Transport Minister Warren Truss said "nothing of note" was found Sunday, which he described as a "fruitless day."
He said that the new search area, based on French radar data that indicated possible debris, was 530 miles north of the previous search zone. He said it was not the same area that had been identified as the most likely place where the aircraft may have entered the sea, "but ... we've got to check out all the options."
"We're just, I guess, clutching at whatever little piece of information comes along to try and find a place where we might be able to concentrate the efforts," he added.
A cyclone bearing down on the Australian northwest coast "could stir up less favorable weather," he said.
An American search crew that spent nine hours Sunday scouring a sector of the massive search area said weather conditions were forcing them to fly extremely low over the water.
"The aircraft was flying down at 300 feet, and visibility was extremely limited," Lt. Cmdr. Adam Schantz told CBS News' Holly Williams.
"It's tough. It's frustrating. But the crews go out and they do the best they can," he said.
Flight 370 vanished March 8 with 239 people aboard while en route from Kuala Lumpur, Malaysia, to Beijing, setting off a multinational search that has turned up no confirmed pieces and nothing conclusive on what happened to the jet.
Australian authorities coordinating the search sent planes and a ship Sunday to try to "re-find" a wooden pallet that appeared to be surrounded by straps of different lengths and colors.
The pallet was spotted on Saturday from a search plane, but the spotters were unable to take photos of it, and a PC Orion military plane dispatched to locate it could not find it.
"So, we've gone back to that area again today to try and re-find it," said Mike Barton, chief of the Australian rescue coordination center. "It's a possible lead," he added.
Wooden pallets are often used by ships, Barton cautioned. But he said airlines also commonly use them in cargo holds.
An official with Malaysia Airlines said Sunday night that the flight was, in fact, carrying wooden pallets. The official spoke on condition of anonymity in keeping with company policy.
AMSA said it has requested a cargo manifest from Malaysia Airlines.
When Brazilian searchers in 2009 were looking for debris from Air France Flight 447 after it mysteriously plunged into the Atlantic Ocean, they found a wooden pallet. The military initially reported the pallet came from the Air France flight, but backtracked hours later and said the plane had not been carrying any wooden pallets.
Sunday's search was frustrating because "there was cloud down to the surface, and at times we were completely enclosed by cloud," Royal Australian Air Force flight Lt. Russell Adams told reporters.
Nothing of interest was found, he said. But he added that the search was worth it because "we might do 10 sorties and find nothing, but on that 11th flight when you find something and you know that you're actually contributing to some answers for somebody."
In Paris, French Foreign Ministry spokesman Romain Nadal said in an interview with The Associated Press that the satellite radar echoes "identified some debris that could be from the Malaysian Airlines plane."
The spokesman said that these echoes "are not images with a definition like a photograph, but they do allow us to identify the nature of an object and to localize it."
"The French government has decided to increase its satellite monitoring of this zone and try to obtain precise images and locations," Nadal said.
Gathering satellite echo data involves sending a beam of energy to the Earth and then analyzing it when it bounces back, according to Joseph Bermudez Jr., chief analytics officer at AllSource Analysis, a commercial satellite intelligence firm.
Satellite radar echoes can be converted into an image that would look similar to a black-and-white photo, though not as clear, he said. "You'd have to know what you're looking at," Bermudez said.
A Malaysian official involved in the search said the French data located objects about 575 miles north of the spots where the objects in the images released by Australia and China were located.
One of the objects located was estimated to be about the same size as an object captured Tuesday by the Chinese satellite that appeared to be 72 feet by 43 feet, said the official, who declined to be identified because he wasn't authorized to speak to the media. It was not possible to determine precise dimensions from the French data, the official said.
The southern Indian Ocean is thought to be a potential area to find the jet because Malaysian authorities have said pings sent by the Boeing 777-200 for several hours after it disappeared indicated that the plane ended up in one of two huge arcs: a northern corridor stretching from Malaysia to Central Asia, or a southern corridor that stretches toward Antarctica.
Malaysian authorities have not ruled out any possible explanation for what happened to the jet, but have said the evidence so far suggests it was deliberately turned back across Malaysia to the Strait of Malacca, with its communications systems disabled. They are unsure what happened next.
Authorities are considering the possibilities of hijacking, sabotage, terrorism or issues related to the mental health of the pilots or someone else on board.