It's day three of the search for Malaysia Airlines flight MH370 -- which vanished over waters between Vietnam and Malaysia early Saturday morning.
Eight countries joined the search for the plane early Saturday, but so far no positive sightings of the jetliner have been made. Malaysia's Department of Civil Aviation said the eight nations have a combined 40 ships and 34 aircraft involved in the hunt.
Several sightings of suspicious objects were reported Saturday and Sunday, including what was believed to be a window or door of the plane. But Azharuddin Abdul Rahman, director general of Malaysia's Department of Civil Aviation, said Monday that nothing has been verified.
"Unfortunately, ladies and gentlemen, we have not found anything that appears to be objects from the aircraft, let alone the aircraft. We will be intensifying our efforts to locate the missing aircraft," he told reporters.
He said some samples of an oil slick spotted in the area are being analyzed to see if they could have come from the aircraft. But according to Azharuddin, the fate of the aircraft remains unknown.
"And as far as we are concerned we equally puzzled as well. The honorable prime minister used the word perplexing. We are equally puzzled as well and to be confirmed what really happened on that particular day, on this ill-fated aircraft, we need hard evidence, we need concrete evidence, we need parts of the aircraft," said Azharuddin.
The jetliner was carrying 239 people, more than 150 of whom were Chinese nationals. China has sent four search and rescue vessels and two warships to help in the mission.
Vietnam dispatched two planes and seven ships to search for the plane, the Ministry of Foreign Affairs said in a statement Monday. The National Committee for Search and Rescue said another five planes and four ships are on standby for search activities.
Greg Waldron, Asia managing editor of Flightglobal, a trade publication for the aviation sector, said he thought the coordination of search and rescue vessels was coming together as an international team effort. He said the challenge is spotting pieces of wreckage.
"The wreckage is very unlikely to show up on radar, and it is also very unlikely to show in infra red, because it has the same temperature as the surface," Waldron explained. "So in terms of finding pieces of the aircraft, if indeed these pieces of aircraft are floating around in the sea, you are really relying on people's eyeballs. And also the wreckage if there is wreckage has had days to spread. And this could make it more challenging to locate."
The United States sent the USS Pinckney, an Arleigh Burke-class guided-missile destroyer, to the area on Sunday. Another vessel is on its way, according to Bleu Moore, spokesman from the 7th Fleet public affairs office.
"We're also sending out the USNS Ericsson. It's on its way there, it's not in the same body of water but its on the way there," said Moore.
He said the biggest challenge is time: the more time passes, the less chance there is to save lives.
It could be a long wait before answers are found. When an Air France jetliner disappeared over the Atlantic on its way from Rio de Janeiro to Paris in 2009, it took investigators nearly two years to find and retrieve the aircraft’s black box data recorders.