Malaysia, reeling from a storm of criticism about its handling of the crisis, sent an aircraft to investigate the reported sighting of three large floating objects in the South China Sea, vowing to pursue all "concrete clues".

The search for Malaysia Airlines flight MH370 — which entered a sixth day Thursday — has been blighted by false alarms, swirling rumours and contradictory statements about its fate, after it disappeared from radar Saturday on a journey from Kuala Lumpur to Beijing.

"Every day it just seems like it's an eternity," Danica Weeks, whose husband Paul was on MH370, told CNN from their home in the Australian city of Perth.

Fighting back tears, she described how Paul had left his wedding ring and watch with her for safekeeping before starting his journey to a mining venture in Mongolia.

"I'm praying that I can give (them) back to him. It's all I can hold onto. Because there's no finality to it and we're not getting any information," she said.

China's state science and technology administration said late Wednesday that a Chinese satellite had captured images of the objects in a suspected crash area on Sunday, and the information was being analysed.

It was not immediately clear why the information has only just come to light. The region is criss-crossed by busy shipping lanes and littered with debris, complicating the search.

Large oil slicks found by Vietnamese planes on Saturday yielded no trace of the Boeing 777 while previous sightings of possible wreckage proved to be false leads.

The search for the plane now encompasses both sides of peninsular Malaysia over an area of nearly 27,000 nautical miles (more than 90,000 square kilometres) — roughly the size of Portugal — and involves the navies and air forces of multiple nations.

Theories about the possible cause of the disappearance range from a catastrophic technical failure to a mid-air explosion, hijacking, rogue missile strike and even pilot suicide.

- 'This could be it' -

The objects detected by the Chinese satellite were seen roughly 200 kilometres (124 miles) east of the location of the plane's last reported contact roughly mid-way between the coasts of Malaysia and Vietnam.

"That would make sense if the debris were there," said Gerry Soejatman, a Jakarta-based independent aviation analyst.

"It is very possible that this could be it. The satellite image is what is seen at the time the debris would have drifted and/or sunk by then. It can be calculated to find where it is now."

The objects were spread across an area on the eastern-most margin of the original search zone, with a radius of 20 kilometres (12 miles), in sizes that appeared to be 13 x 18 metres, 14 x 19 metres and 24 x 22 metres.

Malaysia and Vietnam said they were checking the new information, which could prompt the focus of the search to swing back to the original flight path, after a shift in recent days to Malaysia's west coast — far from the last known location.

"We will look at all areas especially the ones with concrete clues," a spokesman for Malaysia’s civil aviation department said after the Chinese announcement.

But, raising fresh questions about the coordination of the huge search, Vietnam's deputy civil aviation chief Dinh Viet Thang said his country had only seen the report on the Internet and would not send rescue vessels to the site until they received more detailed information.

Army deputy chief of staff Vo Van Tuan said Vietnam would deploy seven boats and three aircraft on Thursday as part of its search efforts.

"These pictures were taken by the Chinese on Sunday but they have only informed us now. We are verifying this information," he said, but declined to specify whether Beijing had officially provided the images.

And the US Navy, which is contributing two destroyers and two surveillance planes to the vast search, appeared to be treating the latest news with caution.

"I do not have specific information about that satellite image," Commander William Marks of the USS Blue Ridge, the command ship of the US Seventh Fleet, told CNN.

- 'Good-quality images' -

The China Centre for Resources Satellite Data and Application said in a statement on its website earlier this week that it had deployed eight land observation satellites to scour the suspected crash area.

By Tuesday morning it had obtained images covering 120,000 square kilometres.

"The quality of the data images is rather good, which laid a good foundation for further analysis," it said.

China has also requested assistance from a fleet of Earth-monitoring satellites under the International Charter on Space and Major Disasters, designed to aid emergency or relief efforts.

Citizen volunteers too have been urged to join the search through a crowdsourcing effort spearheaded by satellite firm DigitalGlobe.

US authorities said their spy satellites had detected no sign of a mid-air explosion.

In a new twist, Malaysian police said Thursday they were investigating the two pilots, after an Australian television report of a past cockpit security breach.

Malaysia Airlines has said it was "shocked" over allegations that First Officer Fariq Abdul Hamid, 27, along with a fellow pilot, violated airline rules in 2011 by allowing two young South African women into their cockpit during a flight.

It also emerged that months before the Malaysia Airlines jet vanished, US regulators had warned of a "cracking and corrosion" problem on Boeing 777s that could lead to a drastic drop in cabin pressure and possible mid-air break-up.

The Federal Aviation Administration circulated a draft of the warning in September and issued a final directive on March 5, three days before MH370 disappeared.