Air force pilots saw metallic objects, plane seats, an orange buoy and jet fuel stains in the water about 650 km (400 miles) north of the archipelago of Fernando de Noronha off Brazil's northeastern coast.
Brazil's navy said a Dutch commercial ship was nearby and would arrive in the area shortly. Brazilian navy ships, one carrying a helicopter, were not expected to arrive in the area until Wednesday.
The chances of finding survivors appeared close to nil and authorities were treating the passenger list as a death toll.
"The plan now is to focus our efforts to collect the debris and try to identify if they belong or not to the Air France plane," Brazilian Air Force Colonel Jorge Amaral told reporters in Brasilia, the capital.
"We can't really say this is part of the airplane. The command center needs to have at least one piece of the debris with a serial number to confirm that it belongs to the airplane."
No Distress Signal
Three Brazilian air force Hercules planes took off from the islands of Fernando de Noronha, which sit about 370 km (230 miles) off the coast of South America, early on Tuesday to look for traces of the Airbus A330.
The area is near where the last contact was made with the flight that took off for Paris from Rio de Janeiro on Sunday night and went missing in storms about four hours later without sending any distress signal.
Brazil's air force last had contact with the plane at 0133 GMT on Monday when it was 565 km (350 miles) from Brazil's coast. The last automated signals were received at 0214 GMT.
If no survivors are found, it would be the worst disaster in Air France's 75-year history and the deadliest since one of the company's supersonic Concorde planes crashed in 2000.
Air France flight 447 sent an automatic message reporting electrical faults before it went missing. But aviation experts said they did not have enough information to understand how a modern plane with an excellent safety record and operated by three experienced pilots could have crashed.
"All scenarios have to be envisaged," French Defense Minister Herve Morin said on Europe 1 radio.
"We can't rule out a terrorist act since terrorism is the main threat to Western democracies, but at this time we don't have any element whatsoever indicating that such an act could have caused this accident," Morin added.
The flight was carrying 216 passengers of 32 nationalities, including seven children and one baby. Sixty-one were French citizens, 58 Brazilian and 26 German. Twelve crew members were also on board.
Race Against the Clock
Senior French minister Jean-Louis Borloo said it was crucial to locate the black boxes, or flight recorders, which are programmed to emit signals for up to 30 days.
"This is a race against the clock," Borloo told RTL radio.
Distraught relatives of the flight's passengers were assisted by teams of psychologists in Paris and Rio.
French electrical equipment firm CGED said 10 of its staff were on the missing plane with their partners after winning a trip to Brazil in the company's annual sales contest.
An Air France spokesman said on Monday that a lightning strike could be to blame for the disaster. But aviation experts said such strikes on planes were common and could not alone explain the downing of a modern aircraft.
Experts were baffled by the absence of any distress messages, either human or automatic, from the plane. No mayday message was picked up, nor were any signals received from emergency beacons that should have transmitted automatically.
"It would be very unusual to have all the communications systems fail at once," said David Gleave of Aviation Safety Investigations, an airport and air traffic control risk management consultancy based in Britain. "That would tend to indicate that something catastrophic happened."
Morin said France had sent three jets, one AWACS or airborne warning and control system, as well as two naval vessels to search for the plane. The United States agreed to help locate the crash site using satellite data.
Air France said the plane, which was powered with General Electric engines, went into service in April 2005. It last underwent maintenance in a hangar in April this year.
