The search for flight 370 goes on

Search and rescue workers may have discovered some wreckage from Malaysia Airlines Flight MH370, which has been missing since early Saturday morning.  [Special coverage]

Late on Sunday, Xinhua News Agency quoted Vietnamese sources as saying a military patrol boat had found "suspicious floating yellow objects" 80 kilometers from the Tho Chu Islands in the Gulf of Thailand. The objects were made of a composite material and may have been part of a porthole, according to Vietnam Youth Daily.

Earlier, the scope of the search for the Boeing 777 carrying 239 people was widened to 10,000 square kilometers on Sunday after reports that the Beijing-bound jet had turned back to Kuala Lumpur before disappearing from radar screens.

Malaysian officials said at a media briefing on Sunday that radar signals indicated the jet had altered course and may have been heading back toward the Malaysian capital when it disappeared. Datuk Azharuddin Abdul Rahman, director-general of Malaysia's Department of Civil Aviation, said the reports had prompted the expansion of the search area to include the west coast of Malaysia.

Also on Sunday, an oil slick was spotted around 80 km southwest of two slicks spotted earlier by Vietnamese Air Force planes. The original slicks, said to be consistent with a crashed aircraft, were later reported to have disappeared.

Chinese rescue ship Taishunyuan failed to find any evidence of debris at the suspected crash site on Sunday morning.

Another Chinese vessel, China Coastguard 3411, was reported to be around 45 nautical miles from the suspected crash site.

Nine countries, including the US, Singapore and Vietnam, have joined the search.

The Malaysia Airlines plane left Kuala Lumpur in the early hours of Saturday morning. It was carrying 239 people, including 154 Chinese nationals, and was supposed to arrive at its destination at 6:30 am, but vanished from radar screens somewhere between the east coast of Malaysia and southern Vietnam.

Interpol confirmed on Sunday that at least two stolen passports — an Austrian and an Italian — were used by passengers on the flight.

The passports were stolen in Thailand in 2012 and 2013, Interpol said. The agency is trying to determine the identities of the passengers who used the stolen passports.

"Whilst it is too soon to speculate about any connection between these stolen passports and the missing plane, it is clearly of great concern that any passenger was able to board an international flight using a stolen passport," said Interpol Secretary General Ronald K. Noble.

In Beijing, the families of the missing passengers were awaiting developments at the Lido Hotel on Sunday. They were being looked after by around 100 Malaysia Airlines staff members.

Speaking at the National People's Congress on Sunday afternoon, Premier Li Keqiang said he was receiving regular updates on developments in the search and rescue operation from relevant departments. "We are doing everything we can. The government not only has to ensure the safety of citizens at home, but must also provide strong support for outbound travelers," he said.

Maritime search and rescue work is different from that undertaken after a land-based disaster such as an earthquake, when the golden period for optimum rescue is about 72 hours, according to Ma Weiming of the Chinese Academy of Engineering.

The water temperature is relatively warm on the surface of the South China Sea, so if any passengers survived the presumed crash, they may have been granted a slightly longer survival period, he said.

Huang Huikang, China's ambassador to Malaysia, said the unusual loss of contact was still a puzzle.