A Malaysia Airlines Boeing 777 reportedly crashed into the sea off Vietnam with 239 people on board on Saturday. It took off from Kuala Lumpur and was bound for Beijing.

Terrorism is being investigated as a possible cause in the mysterious disappearance, after it was discovered that two passengers had apparently been traveling on stolen passports, authorities said Saturday.

U.S. officials said they are investigating terrorist concerns, NBC reported. Malaysian authorities said they have not ruled out the possibility that the missing flight could be terrorist-related.

Vietnamese state media has reported that the aircraft came down near Tho Chu Island. Malaysian authorities have not yet confirmed the crash and say no wreckage has been found. A huge search is underway.

Contact was lost two hours into the flight and anxious relatives at Beijing airport were initially told it had been delayed before confirmation came that it was missing.

The plane disappeared without giving a distress signal.

The vast majority of those on board Malaysia Airlines Flight 370 were Chinese but passengers were of 14 nationalities, among them Malaysians, Australians, Americans and French citizens.

According to Euronews, If the crash is confirmed, it would mark the second fatal accident involving a Boeing 777 in less than a year.