General view of the interior of the cockpit of an A320 aircraft belonging to Jetstar Asia airways, at Singapore airport January 31, 2015.[Photo/Agencies]

"VERY SMOOTH, VERY COOL"

The cockpit audio had showed "very smooth, very cool" conversation between the pilots in the early part of the flight.

"We don't know yet the reason why one of the guys went out," the official said. "But what is sure is that at the very end of the flight, the other pilot is alone and does not open the door."

A spokesman for Germanwings' owner Lufthansa said: "We have no information from the authorities that confirms this report and we are seeking more information. We will not take part in speculation on the causes of the crash."

It confirmed that the main pilot had over 6,000 hours of flying time, while the more junior co-pilot had just 630 hours and had been with Germanwings since September 2013.

In France, the interior and defence ministries said they had no information on the newspaper report. Lufthansa announced it would hold a briefing for later in the day.

France's BEA air investigation bureau was not available for comment. On Wednesday, it said it was too early to draw meaningful conclusions on why the plane went down.

"We have not yet been able to study and to establish an exact timing for all the sounds and words heard on this file," BEA director Remi Jouty told a news conference.

Jouty expected the first basic analysis in days but warned that the read-out could be subject to errors and that more work would be needed for a full interpretation.