China said late Wednesday its satellites had detected three large floating objects in a suspected crash site near where the Malaysia Airlines plane, which disappeared Saturday on a flight from Kuala Lumpur to Beijing with 239 people on board, lost contact.

But Vietnam said Thursday that two of its planes dispatched to the area had found no trace of the airliner.

Reeling from a storm of criticism about its handling of the crisis, Malaysia also sent an aircraft to investigate the reported sighting in the South China Sea, pledging to pursue all "concrete clues" -- but that it had also found nothing as of Thursday afternoon.

"Nil sighting," the Malaysian air force's director-general of operations, Affendi Buang, told AFP.

The search for Malaysia Airlines flight MH370 -- which entered a sixth day Thursday -- has been blighted by false alarms, swirling rumors and contradictory statements about its fate.

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

China will keep up the search "as long as there is a glimmer of hope", Premier Li Keqiang said.

The passengers included 153 Chinese citizens.

It was not immediately clear why the satellite information has only just come to light. The region is crisscrossed 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 kilometers) -- roughly the size of Portugal -- and involves the navies and air forces of multiple nations.

NJF/NJF