The Australian-led mission said five aircraft had been sent back to an area some 2,500 km (1,500 miles) southwest of Perth. The search began on Thursday after analysis of satellite images identified two large objects floating in the ocean there that may have come from the Boeing 777 which went missing 13 days ago with 239 people aboard.
Investigators have said the satellite images were a credible lead but nothing beyond that.
"It's about the most inaccessible spot that you can imagine on the face of the earth, but if there is anything down there, we will find it," Australian Prime Minister Tony Abbott told reporters in Papua New Guineau, where he is on a visit.
"We owe it to the families of those people (on board) to do no less."
The investigators suspect Flight MH370, which took off from Kuala Lumpur for Beijing shortly after midnight on March 8, was deliberately diverted thousands of miles from its scheduled path. They say they are focusing on hijacking or sabotage but have not ruled out technical problems.
The search for the plane also continues in other regions, including a wide arc sweeping northward from Laos to Kazakhstan.
A source close to the investigation said it might take "several days" to establish whether the objects spotted by satellite in the Indian Ocean came from the missing airliner.
A former senior crash investigator said there had been false leads in many investigations, especially in waters containing stray containers or dumped and lost cargo.
Three Australian P3 Orions joined by a high-tech U.S. Navy P8 Poseidon aircraft and a civilian Bombardier Global Express jet to search the 23,000 square km (8,900 sq mile) zone on Friday, the Australian Maritime Safety Authority (AMSA) said. A Norwegian merchant ship that had been diverted to the area on Thursday was still searching there and another vessel would arrive later on Friday.
Australia's weather bureau said conditions in the area had improved from Thursday, when strong winds and rain had hampered the search by Australian, U.S. and New Zealand aircraft, but visibility was still likely to be affected by low cloud.
China's icebreaker for Antarctic research, Xuelong, or Snow Dragon, will set off from Perth to search the area, Chinese state news agency Xinhua cited maritime authorities as saying.
However, Australian authorities said they had not asked for the ship to search the area. About two-thirds of the missing plane's passengers were Chinese nationals.
India said it was sending two aircraft, a Poseidon P8I and a C-130 Hercules, to join the hunt in the southern Indian Ocean on Friday. It is also sending another P8I and four warships to search in the Andamans Sea, where the plane was last seen on military radar on March 8.
There have been many false leads and no confirmed wreckage found from Flight MH370 since it vanished off Malaysia's east coast, less than an hour after taking off.
There has also been criticism of the search operation and investigation, as more than two dozen countries scramble to overcome logistical and diplomatic hurdles to solve the mystery.
Investigators piecing together patchy data from military radar and satellites believe that, minutes after its identifying transponder was switched off as it crossed the Gulf of Thailand, the plane turned sharply west, re-crossing the Malay Peninsula and following an established route towards India.
What happened next is unclear, but faint electronic "pings" picked up by one commercial satellite suggest the aircraft flew on for at least six hours.
A source with direct knowledge of the situation said that information gleaned from the pings had been passed to investigators within a few days, but it took Malaysia more than a week to narrow the search area to two large arcs - one reaching south to near where the potential debris was spotted, and a second crossing to the north into China and central Asia.
The four-day delay in identifying satellite images that may show debris was due to the vast amount of data that needed to be analysed by various agencies, Australian authorities and the U.S. company that collected the images said.
The satellite images, provided by DigitalGlobe, were taken on March 16, meaning that the possible debris could by now have drifted far from the original site. DigitalGlobal said it was continuing to collect images around the region and sharing them with governments.
The relatively large size of the objects would suggest that if they do come from the missing aircraft, it was largely intact when it went into the water.
Still, finding any debris, let alone the "black boxes" that could shed light on what happened, remains incredibly challenging in the remote, deep-sea region known as the Roaring 40s for the frequent storm-force winds in latitudes between 40 and 50 degrees.