The Air France plane that crashed into the Atlantic last month hit the water intact and at high speed but was missing for six hours before an emergency was declared, French investigators said on Thursday.

Evidence from wreckage indicates the plane was broken apart by impact with the water, which it struck facing forwards.

"The plane was not destroyed while it was in flight. It seems to have hit the surface of the water in the direction of flight and with a strong vertical acceleration," said Alain Bouillard, who is leading the investigation on behalf of France's BEA air accident board.

A food galley was found with its shelves compressed towards its base, the floor of a crew rest area was deformed and the tail fin was wrenched off the fuselage -- all in ways that suggest a violent collision with the ocean, officials said.

The cause of the crash is still not known.

Bouillard said control of the flight was supposed to have passed from air traffic controllers in Brazil to their counterparts in Senegal, but that never happened.

He said the pilots of flight AF 447 tried three times to connect to the Senegalese capital Dakar by satellite without success.

It was not until 0830 GMT, more than six hours after a flurry of error messages from the plane's electronic systems, that the plane was officially declared missing by Spain whose airspace it was due to have crossed en route to France.

Asked whether the alleged air traffic fumble may have delayed the search operation, Bouillard said, "It is one of the subjects of our investigation: why so much time elapsed between the last radio contact and declaration of an emergency."

COORDINATION

Aviation officials say it is not uncommon for planes to be out of reach temporarily while crossing the stormy expanse of ocean where the jet crashed, killing all 228 people on board.

But a Brazilian official denied local controllers had failed to hand over responsibility for the aircraft to Senegal.

"The alert that there had probably been an accident was issued by Madrid. Madrid issued that alert because the plane did not reach its airspace, but before that (the plane) had to pass through Dakar. Why was that alert not issued earlier?," Brazilian Air Force Spokesman Henry Munhoz said.

"The BEA made a preliminary interpretation that possibly Brazil did not transfer control of the flight to Dakar, but this did in fact happen. We have a transcript of it, which was even sent to the BEA. We have information that Dakar did receive that transfer," he told Reuters.

BEA officials said Brazil had sent a "coordination message" advising basic details of the plane's progress but did not send a second message formally transferring control of the aircraft.

The contrasting accounts are the second sign of friction in the aftermath of the world's worst air crash in eight years.

The BEA also reiterated unease that France had not yet been granted access to autopsy reports on bodies taken to Brazil and said these would provide helpful clues in the investigation.

Bouillard said the search for the flight recorders, or black boxes, from the Airbus A330 aircraft would continue until July 10. The recorders emit a signal for around 30 days.

After that, France will continue to probe the seabed with remote sonars until August 15.

Despite the disaster, investigators said they did not see any wider concerns that would indicate the need to ground Airbus A330 aircraft.

Speculation has focused on incoherent speed readings provided by the plane's speed sensors, or pitot tubes, which may have disrupted other systems.

Several problems with A330 speed sensors have been reported, including two in the United States recently, but authorities say none has so far led to a significant loss of altitude.

Families of the Air France victims said on Thursday they wanted more information on the error messages sent by the plane in the last minutes of its flight.