A potential breakthrough emerged Sunday when an aircraft scouring waters off southern Vietnam -- part of an international search and rescue effort -- spotted two objects authorities said could be debris from Malaysia Airlines flight MH370.
But Malaysian authorities said there was no confirmation they came from the Boeing 777 which slipped off radar screens early on Saturday, an hour after leaving Kuala Lumpur bound for Beijing.
"Unfortunately ladies and gentleman, we have not found anything that appears to be objects from the aircraft, let alone the aircraft itself," said Malaysia's civil aviation chief Azharuddin Abdul Rahman.
"This unprecedented missing aircraft mystery -- it is mystifying and we are increasing our efforts to do what we have to do," he told a press conference.
Malaysia has launched a terror probe after at least two of the passengers on board were found to have travelled on stolen passports.
But Azharuddin had few answers to the burning questions surrounding the plane's fate. Asked whether it was possible the plane had been hijacked or disintegrated mid-air, he said nothing could be ruled out.
"We are looking at every angle. We are looking at every aspect of what could have happened," he said. "Again, we have to get concrete evidence... we have to find the aircraft."
More than 150 Chinese are among the missing passengers and Beijing's state media on Monday lashed out at Malaysia and its national carrier over their handling of the crisis.
"The Malaysian side cannot shirk its responsibilities," the Global Times newspaper, which is close to the ruling Communist Party, wrote in a scathing editorial. "The initial response from Malaysia was not swift enough."
- China grief -
At a Beijing hotel, Malaysian embassy officials were processing visa applications for families wanting to take up an airline offer to travel to Kuala Lumpur to be closer to the rescue operations.
Scores of relatives made their way into the room, some in groups of five or six, clutching handkerchiefs and wiping away tears from their faces.
Others said they would not go. "There is more we can do here in China," one woman told AFP. "They haven't even found the plane yet."
A team of Chinese officials from government ministries headed for Malaysia on Monday, tasked with investigating the incident and helping family members already there.
As the search entered a third full day, other families of missing passengers gathered at a hotel in Malaysia's administrative capital, Putrajaya, sharing breakfast as they stared intently at television news bulletins.
The search effort has zeroed in on waters off the remote Vietnamese island of Tho Chu, near where two large oil slicks -- suspected to be caused by aircraft fuel -- as well as the suspected debris were spotted on the weekend.
"All night we mobilised our most modern equipment for the search... but we found no sign of the objects," Vice Admiral Ngo Van Phat told AFP of the hunt centred on Vietnam's southwestern tip.
Tests on the oil slick that could indicate whether it came from the missing plane could be completed by later Monday, Malaysian Maritime Enforcement Agency director general Amdan Kurish told AFP.
Malaysian authorities said they were also combing waters closer to their shores, further south of Tho Chu.
A total of 40 ships and 34 aircraft from an array of Southeast Asian countries, China and the United States have been involved in the search, with two Australian surveillance aircraft joining.
- 'Asian features' -
As they scramble to discover what happened, Malaysian officials have said there was a possibility that MH370 may have inexplicably turned back towards Kuala Lumpur.
The plane, captained by a veteran MAS pilot, had relayed no indications of distress, and weather at the time was said to be good.
Questions have also swirled over how at least two passengers boarded the jet on stolen passports, sparking an investigation into possible links with terrorism and a probe into the sale of passports in Thailand -- where the documents were stolen over the past two years.
Two European names -- Christian Kozel, an Austrian, and Luigi Maraldi of Italy -- were listed on the passenger list, but neither man boarded the plane.
Malaysia's Home Minister Zahid Hamidi reportedly said Sunday that the two passengers who did board using those passports looked Asian in appearance.
"I am still puzzled how come (immigration officers) cannot think: an Italian and Austrian but with Asian facial features," Zahid was quoted as saying by Malaysia's national news agency Bernama.
Interpol confirmed that "at least two passports" recorded in its Stolen and Lost Travel Documents database were used by passengers on the Malaysian flight.
The United States has sent an FBI team to help investigate the passengers, but US officials stressed there was as yet no evidence of terrorism.
Malaysia Airlines shares lost 10 percent in early trading Monday as the market reacted to the jet's disappearance.
The incident is a massive blow for the carrier which has haemorrhaged cash for several years amid mounting competition from low-cost rivals such as AirAsia.