Accident investigators need to recover material from flight AF 447 and, crucially, the flight and cockpit voice recorders if they are to establish how it fell into the sea, our correspondent says.
Two Lufthansa jets, which were in the same area as the Air France plane half an hour before it vanished, could provide clues as to what happened, the UN weather agency says.
Plane crews from Brazil, France and other countries had narrowed their search to a zone halfway between Brazil and west Africa, hoping to pick up signals from the Airbus's beacons.
Brazilian air force's Col Jorge Amaral confirms the sighting - translated
Brazilian air force spokesman Col Jorge Amaral said a Brazilian plane had picked up radar signals indicating "floating metallic and non-metallic materials" at 0100 Brazilian time (0400 GMT) on Tuesday.
At about 0530 Brazilian time, a plane spotted debris in two locations approximately 60km apart.
"In this area, they saw an orange buoy, an aeroplane seat, small white pieces, an aeroplane drum as well as oil and kerosene," Col Amaral told reporters in Rio.
"The search is continuing because it's very little material in relation to the size [of the Airbus A330]."
Col Amaral was also quoted by the Associated Press as saying a life jacket had been spotted amid the debris.
"The locations where the objects were found are towards the right of the point where the last signal of the plane was emitted," he said.
Flight AF 447 left Rio at 1900 local time (2200 GMT) on Sunday
Airbus A330-200 carrying 216 passengers and 12 crew
Contact lost 0130 GMT
Missed scheduled landing at 1110 local time (0910 GMT) in Paris
"That suggests that it might have tried to make a turn, maybe to return to Fernando de Noronha, but that is just a hypothesis."
Searchers now planned to focus their efforts on collecting the debris and trying to identify it, the spokesman said.
At least two cargo ships in the area have been asked to go where the debris was found and are expected to arrive soon, Brazilian officials said.
France is also sending a research ship equipped with two mini-submarines to the search area.
The mini-subs on the Pourquoi Pas can work at depths of up to 6,000m and the area where the plane disappeared has maximum depths of 4,700m (15,400 ft), French naval experts told AFP news agency.
Prime Minister Francois Fillon told the French parliament that the cause of the plane's loss had still to be established.
"Our only certainty is that the plane did not send out any distress call but regular automatic alerts for three minutes indicating the failure of all systems," he said.
Experts remain puzzled that there were no radio reports from the Airbus and they say that such a modern aircraft would have had to suffer multiple traumas to plunge into the sea, our correspondent says.
The two Lufthansa aircraft recorded data on prevailing temperatures and winds, the World Meteorological Organisation (WMO) said.
She was a truly wonderful, exciting girl
John Butler, father of Irish passenger Aisling Butler
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