The Australian-led search of the massive area 2,500km southwest of Perth has resumed after Australian and US aircraft on Thursday failed to locate the two objects photographed by a satellite earlier in the week.
Four military aircraft - two Royal Australian Air Force Orions, a New Zealand Orion and a US Navy P8 Poseidon - are scouring the area on Friday.
The Norwegian merchant vessel St Petersburg remains in the area and another merchant vessel is expected to arrive Friday night. The navy's HMAS Success is also en route and expected to arrive on Saturday.
"To date, no sightings have been reported," AAP quoted the Australian Maritime Safety Authority as saying on Friday.
Acting Prime Minister Warren Truss said the search would be "difficult and challenging", particularly because the objects could have drifted since the satellite spotted them.
The government had cautioned that while the satellite images were "credible", the objects might turn out to be unrelated to the plane.
Prime Minister Tony Abbott told reporters in Papua New Guinea on Thursday that it was the most promising lead so far in the search for flight MH370, which disappeared with 239 people on board almost two weeks ago.
"We don't know what that satellite saw until we get a much closer look at it, but this is the most tangible clue in what's been an utterly baffling mystery.
"We are throwing all the resources we can at it. We will do everything we humanly can to try to get to the bottom of this," he had said.