(CNN) — The crew of a Chinese plane searching for the missing Malaysia Airlines Flight 370 reported that it spotted "suspicious objects" in the southern Indian Ocean on Monday, the latest lead in a long and often frustrating investigation.
But a high-tech U.S. aircraft that followed up on the sighting couldn't find the objects again, Australian authorities said.
A reporter on board the Chinese plane for China's official news agency Xinhua said the search team saw "two relatively big floating objects with many white smaller ones scattered within a radius of several kilometers," the agency reported.
The Chinese plane was flying at 33,000 feet on its way back to Australia's west coast when it made the sighting, the Australian Maritime Safety Authority said.
A U.S. Navy P-8 Poseidon aircraft, one of the military's most sophisticated reconnaissance planes, that was tasked to investigate the objects was unable to relocate them, the authority said.
The IL-76 plane that reported the objects is one of two Chinese military aircraft helping scour a remote area of the southern Indian Ocean on Monday for traces of the passenger jet, which disappeared over Southeast Asia on March 8 with 239 people on board.
With the search in its third week, authorities have so far been unable to establish where exactly the plane is or why it flew off course from its planned journey from Kuala Lumpur to Beijing.
China has a particularly large stake in the search: its citizens made up about two thirds of the 227 passengers on the missing Boeing 777. Beijing has repeatedly called on Malaysian authorities, which are in charge of the overall search, to step up efforts to locate the plane.
A Chinese icebreaker in the region, the Xuelong, has changed course and is headed toward the area where the objects were seen by the Chinese plane, Xinhua said.
Satellites focus search
Recent information from satellites identifying objects in the water that could be related to the plane has focused search efforts on an area roughly 1,500 miles southwest of the Australian city of Perth.
A total of 10 aircraft -- from Australia, China the United States and Japan -- are tasked with combing the search area over the course of Monday.
The aerial searches have been trained on the isolated part of ocean since last week, when Australia first announced that satellite imagery had detected possible objects that could be connected to the search.
Since then, China and France have said they also have satellite information pointing to floating debris in a similar area. The Chinese information came from images, and the French data came from satellite radar.
But Australian officials have repeatedly warned that the objects detected in satellite images may not turn out to be from the missing plane -- they could be containers that have fallen off cargo ships, for example.
On Saturday, searchers found a wooden pallet as well as strapping belts, Australian authorities said. The use of wooden pallets is common in the airline industry, but also in the shipping industry.
The investigation into the passenger jet's disappearance has already produced a wealth of false leads and speculative theories. Previously, when the hunt was focused on the South China Sea near where the plane dropped off civilian radar, a number of sightings of debris proved to be unrelated to the search.
Plane said to have flown low
The sighting of the objects of interest by the Chinese plane came after a weekend during which other nuggets of information emerged about the movements of the errant jetliner on the night it vanished.
Military radar tracking shows that after making a sharp turn over the South China Sea, the plane changed altitude as it headed toward the Strait of Malacca, an official close to the investigation into the missing flight told CNN.
The plane flew as low as 12,000 feet at some point before it disappeared from radar, according to the official. It had reportedly been flying at a cruising altitude of 35,000 feet when contact was lost with air traffic control.
The sharp turn seemed to be intentional, the official said, because executing it would have taken the Boeing 777 two minutes -- a time period during which the pilot or co-pilot could have sent an emergency signal if there had been a fire or other emergency onboard.
Authorities say the plane didn't send any emergency signals, though some analysts say it's still unclear whether the pilots tried but weren't able to communicate because of a catastrophic failure of the aircraft's systems.
The official, who is not authorized to speak to the media, told CNN that the area the plane flew in after the turn is a heavily trafficked air corridor and that flying at 12,000 feet would have kept the jet well out of the way of that traffic.
Malaysia disputes reprogramming
Also over the weekend, Malaysian authorities said the last transmission from the missing aircraft's reporting system showed it heading to Beijing -- a revelation that appears to undercut the theory that someone reprogrammed the plane's flight path before the co-pilot signed off with air-traffic controllers for the last time.
That reduces, but doesn't rule out, suspicions about foul play in the cockpit.
The new details give more insight about what happened on the plane, but don't explain why the plane went missing or where it could be.
Analysts are divided about what the latest information could mean. Some argue it's a sign that mechanical failure sent the plane suddenly off course. Others say there are still too many unknowns to eliminate any possibilities.
CNN aviation analyst Miles O'Brien called the fresh details about the flight a "game changer."
"Now we have no evidence the crew did anything wrong," he said. "And in fact, now, we should be operating with the primary assumption being that something bad happened to that plane shortly after they said good night."
If a crisis on board caused the plane to lose pressure, he said, pilots could have chosen to deliberately fly lower to save passengers onboard.
"You want to get down to 10,000 feet, because that is when you don't have to worry about pressurization. You have enough air in the atmosphere naturally to keep everybody alive," he said. "So part of the procedure for a rapid decompression ... it's called a high dive, and you go as quickly as you can down that to that altitude."
Flight makes emergency landing
Adding to the negative publicity that has blighted Malaysia Airlines since news of Flight 370's disappearance, one of the carrier's passenger jets made an emergency landing in Hong Kong on Monday.
The plane, scheduled to fly from Kuala Lumpur to Incheon, South Korea, was diverted to Hong Kong after its main electrical generator stopped working. Electrical power continued to be supplied by the plane's auxiliary power unit, Malaysia Airlines said
The Airbus A330-300 landed safely at Hong Kong airport around 3 a.m., and the 271 passengers on board have been transferred onto flights with other airlines.
CNN's Sara Sidner, Catherine E. Shoichet, Evan Perez, Kyung Lah and Jaime A. FlorCruz contributed to this report.