Paris- Investigators trying to clarify Thursday's crash of an Airbus A320 plane in the Mediterranean Sea have located the plane's black box, officials said Saturday, but its early recovery was doubtful as heavy sea conditions continued.

A spokeswoman for marine authorities in Toulon told Deutsche Presse-Agentur dpa that it was uncertain whether the planned recovery of the black box by robots could be accomplished over the weekend.

The plane, just three years old, went down as it was making its landing approach at the coastal city of Perpignan after a two-hour test flight.

There had been no distress signal beforehand, and moments before, air traffic controllers had held normal communications with the cockpit crew.

Eyewitnesses spoke how the plane suddenly climbed steeply, only then to plunge like a rock into the 40-metres-deep waters.

Weather conditions were good, but temperatures were cold, leading to speculation about whether the plane's wings or rudder had suddenly iced up.

The plane belonged to Air New Zealand and had been leased to the German carrier XL Airways for the last two years. It was to have been returned in the coming days to Air New Zealand following completion of the maintenance work, a spokesman for XL Airways said.

Seven people are believed dead in the crash. Two bodies were recovered from the waters on Thursday before the search was called off because of heavy rains and high waves. Bad weather hampered search efforts on Friday.

Two German pilots, a pilot and three engineers employed by Air New Zealand as well as an inspector from New Zealand's Civil Aviation Authority were aboard the aircraft. (dpa)