One day after Malaysia Airlines flight MH370 went missing, multi-nation search and rescue operations in the South China Sea resumed on Sunday morning. So far, no trace has been found of the missing plane, which vanished with 239 people on board.

Speculation is rife on social media, with experts and commentators discussing possibilities such as a terrorist plot, twin-engine failure, hijacking, the plane landing somewhere safely and even pilot suicide.

Reports that two of the passengers in the jetliner had apparently boarded the midnight flight from Kuala Lumpur to Beijing on stolen passports set off terrorism alarms.

The Boeing 777's excellent safety record, Malaysia Airlines' reputation as one of the safest airlines in Asia and the fact that no distress signal was sent while flying at an altitude of 35,000ft gave rise to speculation that foul play had brought the plane down.

Malaysian civil aviation authorities said Sunday morning there was still no official explanation for the plane's disappearance. Officials said no wreckage has been located. The missing aircraft has been in service for 15 years and logged about 20,000 flying hours.

"There is nothing to report at this juncture ... The rescue operations continue... and we have to report that we have not been able to locate anything," Azharuddin Abdul Rahman of Malaysia's civil aviation authority told a new gathering in Kula Lumpur.

A statement on Malaysia Airlines' website exhorted people to pray for the flight and said the airline authorities were providing support to the distressed relatives.

"It is very puzzling right now ...We have conflicting very early lines of evidence," John Cox, an accident investigator and chief executive officer at Safety Operating Systems told Bloomberg News.

Twelve hours after the plane lost radio contact with air traffic control while it was overflying Vietnam and about two hours short of its destination, Beijing International airport, an oil slick 9 miles long was reportedly spotted off the Vietnam coast by the military, seemingly confirming fears of a crash into the sea.

However, Malaysia Airlines stopped short of confirming a crash, as did Malaysian authorities who said the focus was on attempts to locate the plane.

Terror strike downed the plane?

Malaysian Prime Minister Najib Razak did not rule out a terrorist plot that might have brought down the plane.

"We are looking at all possibilities, but it is too early to make any conclusive remarks," Razak said, according to the BBC.

Experts have said a terror attack is one of the strong possibilities, though no specific leads have emerged and no militant outfit has claimed responsibility for the attack.

Reports have linked the disappearance of the plane, with 154 Chinese on board, with a mass stabbing attack allegedly carried out by separatist Uighur militants in Kunming in Chinas' restive south-west.

John Magaw, a former US transportation-security official, told Bloomberg an over-water disappearance and stolen passports raised huge red flags. "Those two things right there are highly, highly, highly suspicious," the expert said.

Aircraft's maintenance record under scanner

Another angle explored by airline security experts is the aircraft's safety and maintenance records, even though Malaysia Airlines has a strong safety record.

Barring a bomb explosion or a similar terrorist attack, the only other reason behind a sudden disappearance of the jet without any warning from the crew could be an unusual and large-scale mechanical failure.

Malaysian civil aviation experts will be helped by the US National Transportation Safety Board (NTSB) in analysing the maintenance record of the aircraft.

There will be intense focus on the loss-making airline's recent safety maintenance record and if financial challenges and rising competition from low cost carriers had affected safety measures.

The struggling airline posted a net loss of MRY1.17 billion ($356 million) in 2013, a threefold rise in losses from the previous year.

"The full-year performance of [Malaysia Airlines] making a bigger loss in 2013 compared to 2012 demonstrates the challenges brought on by intensifying competition leading to lower yields for all players," Ahmad Jauhari Yahya, Malaysia Airlines Group CEO, said at the time.