Australia promised its best efforts to resolve the mystery, but two days of searching the seas about 2,500 kilometers (1,550 miles) southwest of Perth have not produced any evidence.
A satellite spotted two large objects in the area earlier this week, raising hopes of finding the Boeing 777 that disappeared March 8 with 239 people on board.
Australia's Acting Prime Minister Warren Truss told reporters in Perth on Saturday that "so far, there have been no findings of note."
"It is a very remote area, but we intend to continue the search until we're absolutely satisfied that further searching would be futile — and that day is not in sight," he said.
Bad weather hindered Friday's search but conditions in the southern Indian Ocean improved Saturday, Prime Minister Tony Abbott said in Papua New Guinea. He said that six aircraft were in the area plus an Australian naval vessel on the way.
The aircraft included two ultra long-range commercial jets and four P3 Orions, the Australian Maritime Safety Authority said.
Because of the distance to the area, the Orions will have enough fuel to search for two hours, while the commercial jets can stay for five hours before heading back to the base.
Two merchant ships were in the area, and the HMAS Success, a navy supply ship, was due to arrive late Saturday afternoon. Weather in the search zone was expected to be relatively good, with some cloud cover.
Two Chinese aircraft are expected to arrive in Perth on Saturday to join the search, and two Japanese planes will arrive Sunday. A small flotilla of ships from China is still several days away. The Malaysian plane passengers included 154 Chinese.
AMSA officials also were checking to see if there was any new satellite imagery that could provide more information. The satellite images were taken March 16, but the search in the area did not start until Thursday because it took time to analyze them.
In Kuala Lumpur, where the Flight 370 plane took off for Beijing, Malaysian Defense Minister Hishammuddin Hussein called the process "a long haul" as he thanked the more than two dozen countries involved in a search that stretches from Kazakhstan in Central Asia to the southern Indian Ocean.
The Telegraph newspaper in London carried a report showing a transcript of the conversation between the pilots and traffic control before the plane disappeared. The paper said it may have been noteworthy because one of the pilots repeated his altitude about the same time a transponder was turned off.
Peter Marosszeky, an aviation expert at the University of New South Wales in Australia, cautioned against reading too much into the transcript as pilots occasionally repeat themselves.
"I've sat through many thousands of flights myself and it's not something that would really strike me as unusual," he said.
Without being able to hear the inflection in the pilots' voices, it's very difficult to determine whether anything said is truly noteworthy, he added.
"I'd love to hear the actual voice level of communication to see if there's any level of anxiety that might have been driving the pilot to say what he did," he said.
Malaysia asked the U.S. for undersea surveillance equipment to help in the search, said Rear Adm. John Kirby, a Pentagon spokesman. Defense Secretary Chuck Hagel promised to assess the availability of the technology and its usefulness in the search, Kirby said.
The Pentagon says it has spent $2.5 million to operate ships and aircraft in the search and has budgeted another $1.5 million for the efforts.
There is a limited battery life for the beacons in the cockpit-voice and flight-data recorders — about 30 days, said Chuck Schofield, vice president of business development for Dukane Seacom Inc. He said it's "very likely" that his company made the beacons on the missing jet.
The devices work to a depth of 20,000 feet (6,096 meters), with a signal range of about 2 nautical miles (2.3 miles; 3.7 kilometers), depending on variables like sea conditions. The signals are located using a device operated on the surface of the water or towed to a depth.
Experts say it is impossible to tell if the grainy satellite images of the two objects — one 24 meters (almost 80 feet) long and the other measuring 5 meters (15 feet) — were debris from the plane. But officials have called this the best lead so far in the search that began March 8 after the plane vanished over the Gulf of Thailand on an overnight flight to Beijing.
For relatives of those aboard the plane, hope was slipping away, said Nan Jinyan, sister-in-law of passenger Yan Ling.
"I'm psychologically prepared for the worst and I know the chances of them coming back alive are extremely small," said Nan, one of dozens of relatives gathered at a Beijing hotel awaiting any word about their loved ones.
The Norwegian cargo vessel Hoegh St. Petersburg is also in the area helping with the search. Haakon Svane, a spokesman for the Norwegian Shipowners' Association, said the ship had searched a strip of ocean stretching about 100 nautical miles (115 miles; 185 kilometers).
Some questions had been raised about the cargo of the missing plane because it contained lithium ion batteries. Malaysia Airlines issued a statement saying they were in compliance with the International Civil Aviation Organization and the International Air Transport Association requirements and classified as "non-dangerous goods."
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.
Police are considering the possibilities of hijacking, sabotage, terrorism or issues related to the mental health of the pilots or anyone else on board.
By KRISTEN GELINEAU and ROB GRIFFITH (AP)