Malaysia Airlines plane that has been missing for more than 24 hours may have turned back, radar signals showed.

Rescue teams looking for the plane have now widened their search area.

Investigators are also checking CCTV footage of two passengers who are believed to have boarded the plane using stolen passports.

Flight MH370 from Kuala Lumpur to Beijing disappeared south of Vietnam with 239 people on board.

Air and sea rescue teams have been searching an area of the South China Sea south of Vietnam for more than 24 hours.

Malaysia’s civil aviation chief, Azharuddin Abdul Rahman, told a press conference in Kuala Lumpur the search area had been expanded, to include the west coast of Malaysia.

Five passengers booked on the flight did not board, he added. Their luggage was consequently removed.

Twenty-two aircraft and 40 ships are now involved in the search, armed forces chief Gen. Zulkefli Zin said.

Air force chief Rodzali Daud said the investigation was now focusing on a recording of radar signals that showed there was a “possibility” the aircraft had turned back from its flight path.

Vietnamese navy ships which reached two oil slicks spotted earlier in the South China Sea found no signs of wreckage.

Malaysia’s Transport Minister, Hishammuddin Hussein, initially said at least four names on the passenger list were “suspect”.

However, he later said there were in fact only two suspect names.

Reports suggest two of the passengers listed as travelling – an Italian and an Austrian – were not actually on the flight.

They had both reportedly had their passports stolen in Thailand in recent years.

Hishammuddin Hussein said international agencies including the FBI had joined the investigation and all angles were being examined.

The passengers on the flight were of 14 different nationalities. Two-thirds were from China, while others were from elsewhere in Asia, North America and Europe.

When he was asked earlier whether terrorism was suspected as a reason for the plane’s disappearance, Malaysian PM Najib Razak said: “We are looking at all possibilities but it is too early to make any conclusive remarks.”

Malaysia Airlines plane vanished at 01:30 local time on Saturday, March 8.

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According to new reports, US officials are investigating terrorism concerns after revelations that two people apparently boarded the missing Malaysia Airlines jetliner with stolen passports.

The officials told NBC News that they had found no clear link to terrorism. There are other criminal reasons, for example drug smuggling, that stolen passports might be used to board a plane.

Two names on the passenger manifest of the plane, Malaysia Flight 370, matched passports reported stolen in Thailand, one from an Italian man and the other from an Austrian man, according to foreign governments.

The news, hours after the Malaysia Airlines jet disappeared over the South China Sea with 239 people on board, significantly changed how US officials looked at the disaster. The officials said they were checking into passenger manifests and going back through intelligence.

There was still no sign of wreckage more than 24 hours after air traffic controllers lost contact with the plane, a red-eye from Kuala Lumpur, Malaysia, to Beijing.

The aircraft vanished in relatively clear weather, without sending a distress signal, at what analysts said would have been cruising altitude. In a possible clue, Vietnamese planes spotted two oil slicks consistent with jet fuel in the water off Vietnam.

On board were 227 passengers and 12 crew. Most of the passengers were Chinese. Three were Americans – one adult and two children, according to the passenger manifest.

Search teams from Malaysia, Vietnam, Singapore and China were looking for wreckage, and the US sent a naval destroyer into the South China Sea to help. The air search was called off during the night but was to resume at daylight Sunday, or early Saturday evening Eastern time.

The Italian on the passenger list was Luigi Maraldi, 37. His father, Walter Maraldi, told NBC News on Saturday that Luigi was vacationing in Thailand and had called to check in.

Walter Maraldi said his son had his passport stolen a year ago in Thailand.

In Austria, the foreign ministry confirmed that police had made contact with a citizen who was also on the passenger list, and who reported his passport stolen two years ago.

“We believe that the name and passport were used by an unidentified person to board the plane,” a spokesman for the ministry said.

It is unusual, but not unheard of, for one person to board a plane with a stolen passport. It is very rare for two people with stolen passports to board the same plane, terrorism analysts say.

Asked earlier whether terrorism was suspected in the disappearance of the jet, Malaysian PM Najib Razak said authorities were “looking at all possibilities,” The Associated Press reported.

Malaysia has not seen significant terrorist activity, and airport security there has tended to be exemplary.

The investigation will probably take some time, partly because authorities would have to find wreckage and perform forensics tests. In the crash of TWA Flight 800, in 1996, it took more than a year to rule out terrorism.

While flight data recorders and cockpit voice recorders, the so-called black boxes, can emit signals from underwater, it can be extremely difficult to find planes that disappear over the sea.

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