PARIS: Search teams hunting an Air France plane that vanished with 228 people on board were scouring remote Atlantic waters 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 plane after it hit heavy turbulence, two Brazilian aircraft with night sensors swept a patch of the Atlantic Ocean almost halfway between South America and Africa.

Officials determined the zone some 1,100 kilometres (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 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 prospects of finding any survivors are very slim," a grim-faced French Sarkozy said after talking to stunned relatives of missing passengers. "It's a catastrophe the likes of which Air France has never seen." US President Barack Obama pledged his country's help in probing the incident.

The flight disappeared early 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 pushed ahead overnight using a Hercules C130 transport with equipment to detect the plane's emergency beacon and another aircraft 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 meant 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 weather conditions and the error messages.

Brazilian President Luiz Inacio Lula da Silva said he held out hope for survivors, but added that earlier he had spoken with Sarkozy by telephone "and really it was an exchange of condolences." If it is confirmed that all 228 people on Flight AF 447 are dead, it would mark the worst loss of life in Air France's history and civil aviation's worst accident for more than a decade.

Spanish and French air forces also sent out search planes to scour a vast area of ocean between Brazil and Africa. In response to a request for assistance from Paris, the United States dispatched a surveillance aircraft and an Air Force search and rescue team.

At Charles de Gaulle airport in Paris and at Tom Jobim International Airport in Rio, tearful relatives were ushered into private areas to await developments and receive counselling away from news media.

In Rio, Vasti Ester van Sluijs told AFP she had jumped into a taxi as soon as she heard the flight had disappeared.

"My daughter Adriana Francesca was on the plane," she said.

Air France said the 216 passengers included 126 men, 82 women, seven children and a baby. There were 12 French crew members.

The passengers hailed from 32 countries, including 61 from France, 58 from Brazil and 26 from Germany.

French Environment Minister Jean-Louis Borloo, whose portfolio includes transport, said hijacking had been ruled out.

Airbus said the A330 has a good safety record, with no fatal accidents on a commercial flight. One did crash in 1994 during a test flight in southern France, however, killing all seven people on board.