Search teams hunting an Air France plane that vanished with 228 people on board were scouring remote Atlantic waters on Tuesday with scant hope of finding survivors and few clues to explain the crash.
As investigators puzzled over a series of error messages sent by the jet after it hit a fierce storm, Brazilian and French spotter planes battled foul weather to sweep a patch of ocean halfway between South America and Africa.
Officials have identified a zone some 1,100 kilometers (680 miles) off Brazil's northeastern coast based on the last signal from Air France flight AF 447, an automatic warning of multiple electric and pressurisation failures.
French President Nicolas Sarkozy and others warned there was very little hope of survivors from what appears to be the worst air accident in over a decade and the worst loss of life in Air France's history.
"The search will continue as long as necessary. All means are deployed in the area and we'll put as many assets at their disposal as necessary," French Defence Minister Herve Morin said in an interview with Europe 1 radio.
A civilian Brazilian pilot flying for TAM airlines reported seeing orange glimmers on the surface of the ocean under Senegalese airspace, but the French military's spokesman could not immediately confirm the sighting.
"We received this information at around 4.30am (0230 GMT) from a Brazilian pilot who said he'd seen faint glows on the surface, in an area consistent with the A330's last reported position," said Captain Christophe Prazuck.
Prazuck said that a French surveillance plane had flown from Cap Verde back along the missing jet's expected flightpath to its last known position.
"We didn't find anything, but the weather was terrible, with what we call a tropical convergence front," he said, describing a phenomenon in which weather fronts from the northern and southern hemispheres clash violently.
Environment Minister Jean-Louis Borloo, whose brief includes the transport portfolio, said that if they wished the relatives of the missing passengers could be flown to the zone of the tragedy to watch the search.
US President Barack Obama pledged his country's help in the search.
The flight disappeared early on Monday four hours into its 11-hour flight from Rio de Janeiro to Paris after the Airbus A330 flew into a storm.
A daytime search by eight Brazilian air force aircraft doing visual sweeps did not turn up anything.
The search continued overnight with a transport aircraft fitted with equipment to detect the plane's emergency beacon and another with onboard radar and infrared gear that could detect bodies in the water.
While the cause of the crash remained a mystery, Air France's chief executive said the aircraft had sent a series of error messages.
"A succession of a dozen technical messages" sent by the aircraft around 0215 GMT showed that "several electrical systems had broken down" which caused a "totally unprecedented situation in the plane," said Pierre-Henry Gourgeon.
"It is probable that it was shortly after these messages that the impact in the Atlantic came," he told reporters at Charles de Gaulle airport, where the flight was scheduled to have landed on Monday morning.
Airline officials had earlier said the plane was probably hit by lightning, but Gourgeon declined to make a direct link between the horrendous weather conditions and the error messages.
"All possibilities must be examined. We cannot, by definition, exclude a terrorist attack, because terrorism is the main threat for all Western democracies," defence minister Morin said.
"But today we have no evidence whatsoever of the cause of the accident."
The 216 passengers included 126 men, 82 women, seven children and a baby. There were 12 French crew members while the passengers came from 32 countries, including 61 from France, 58 from Brazil and 26 from Germany.