The Malaysia Airlines plane that disappeared over the South China Sea is an "unprecedented missing aircraft mystery", according to the head of Malaysia's Civil Aviation Department.
Fears are growing the plane may never be found, as authorities said they had intensified the search, involving 46 ships and 34 planes from nine countries. But no debris has been identified as belonging to the plane.
However ships are being sent from Malaysia to investigate a "yellow object" spotted in Vietnamese waters.
Officials still hope samples will be shown, in chemical tests, to be from the aircraft, but oil spills are not uncommon in the cargo-heavy South China sea.
Azaharuddin Abdul Rahman, the civil aviation head said that "positive evidence" was still needed and no one was planning on giving up the search.
“Unfortunately, we have not found anything that appears to be an object from the aircraft, let alone the aircraft,” he said.
"We will take as long as it takes to locate the plane.
“There are many theories that have been said in the media; many experts around the world have contributed their expertise and knowledge about what could happen, what happened.
"We are puzzled as well."
“We are every hour, every minute, every second looking at every inch of the sea,” he added.
Hijacking has still not been ruled out as a possible explanation, nor the theory that the plane had turned back two hours into the six-hour flight.
The Boeing 777 disappeared with 239 people, including six Australians and two New Zealanders, on board the flight from Kuala Lumpur for Beijing, on Sunday night, and the pilots did not send a distress call.
Two passengers were travelling on stolen European passports - though experts have said that fraudulent use of documents could well be easily explained, with the passports often sold for migration purposes.
The passports were stolen from Luigi Maraldi and Christian Kozel in the last two years, and were listed as stolen on Interpol’s database.
An editorial in the Chinese state-run Global Times newspaper has attacked the airline and authorities on Monday, for a lack of clear information: “The Malaysian side cannot shirk its responsibilities. The initial response from Malaysia was not swift enough.
“There are loopholes in the work of Malaysia Airlines and security authorities. If it is due to a deadly mechanical breakdown or pilot error, then Malaysia Airlines should take the blame. If this is a terrorist attack, then the security check at the Kuala Lumpur airport and on the flight is questionable.
"If it is due to some natural or uncontrollable factors, all airlines across the world including Malaysia Airlines should draw a lesson."Suggest a correction