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A Vietnam Air Force search and rescue aircraft takes part in a mission to find the missing Malaysia Airlines flight MH370, off Vietnam's Tho Chu island Reuters

Four days on, the missing Malaysia Airlines flight MH370 en route to Beijing from Kuala Lumpur is yet to be found.

What could have made the flight with 239 people (227 passengers and 12 cabin crew) aboard just vanish out of the blue?

The theories of the flight's disappearance are adding to several conspiracy speculations as search and rescue teams are turning empty-handed.

Take a look at some of the conspiracy theories, the facts that support them as well as the contradictory factors related to flight MH370 that has vanished mysteriously:

Terror Explosion

Fact: Two people boarded the Beijing-bound airliner with stolen passports.

Theory: An explosion by the two passengers (supposedly terrorists) in the mid-air could have torn the airliner parts apart and thrown them to far distances, making it difficult for the search teams to find any debris.

Contradiction: If the plane had exploded, why no debris has been detected on the air traffic control radar?

Mid-Air Crash

Fact: Avian experts do not rule out the possibility of a mid-air technical failure either.

Theory: "Well I don't have a 360 degree appreciation of every angle. But the more I listen and read, it still comes back down to four key scenarios: the aircraft has suffered some catastrophic mechanical and electrical failure, adverse weather conditions, the aircraft has been blown up in mid-air by terrorists, or it's been forced to land, again by terrorists," Owen Geach, commercial director of the International Bureau of Aviation and one of Britain's leading authorities on air safety, told IBTimes UK.

Contradiction: Malaysia Airlines has an excellent safety record and it has passed a stringent recent safety audit, according to Geach.

Hijacked by Terrorists

Fact: Several of the passengers' mobile phones rang when called by relatives, Chinese media reported. According to the reports, the mobile phones got connected several times but were never answered.

Theory: Unanswered mobile phones suggest that flight MH370 might have been hijacked by the terrorists and forced to land.

Contradiction: If at all there was a threat of hijacking, why the pilot did not send out a mayday signal?

Besides, there are some logical, weird or plain absurd theories that have been doing the rounds:

Alien Abduction

Social media is abuzz with a spooky theory that flight MH370 has been abducted by aliens or UFOs. People have also cited possibility of space debris hitting the flight. Some of the tweets getting viral on Twitter say:

'Vietnamese Bermuda Triangle'

Malaysia's opposition politician Mohammad Nizar Jamaluddin made perhaps the most absurd comment on the vanished flight MH370 as he wrote about a "new bermuda triangle" in Vietnam waters.

Nizar wrote on Twitter: "new bermuda triangle detected in vietnam waters, well equipped sophisticated devices are of no use!" while responding to a tweet by television host Piers Morgan.

Malaysia Airlines Flight MH370