Singapore, China, the U.S. and Vietnam are sending ships and planes in efforts to find the missing Malaysia Airlines flight that was carrying 227 passengers and 12 crew from Kuala Lumpur to Beijing.

Malaysia urgently sent 15 aircrafts and nine ships, and China, with 152 Chinese or Taiwanese nationals on board the missing aircraft, sent a search and rescue plane and a warship.

Singapore, which neighbors Malaysia, sent two warships and a naval helicopter to help in the six-country search. A C130 Hercules -– a transport aircraft with search-and-locate functions -– was deployed on Saturday, the Ministry of Defense spokesman told The Straits Times. The Republic of Singapore Navy also said on its Facebook page on Sunday that its frigate, missile corvette and Sirkorsky S-70B naval helicopter have joined in the search since 2 a.m. It added that its SSRV MV Swift Rescue submarine was preparing for the operation through the night and would join in later on Sunday.

The U.S. dispatched a naval destroyer, USS Pinckney, and a surveillance plane, according to AFP. The Pinckney, carrying two helicopters that can be equipped for search and rescue, was already conducting training and maritime security operations in international waters of the South China Sea, according to the Pentagon. The U.S. military statement said a P-3C Orion reconnaissance plane would also depart shortly from Kadena Air Base in Okinawa, Japan, aiding the effort with additional long-range search, radar and communications capabilities, AFP reported.

The reason for the Malaysian flight going missing is yet to be confirmed. However, The Straits Times reported that the U.S. officials were probing terror concerns following reports that two imposters could have boarded the missing plane.

Christian Kozel, 30, from Austria and Luigi Maraldi, 37, from Italy were in the manifest issued by Malaysia Airlines, but the foreign ministries in both Rome and Vienna confirmed that the men were in their respective countries. Both passports had been stolen in Thailand, NBC News reported.

The U.S. officials told NBC News that they had found no clear link to terrorism and that there could be other criminal reasons such as drug smuggling. The officials also did not clarify the cause of missing flight, saying “it’s still very early,” but indicated that they are not canceling the terror concerns.

Malaysian Prime Minister Najib Razak told The Straits Times that authorities were “looking at all possibilities.”

By Ha Ji-won, Intern reporter (jiwonha@heraldcorp.com)