[SEYNE-LES-ALPES, France] With a new road built to the crash site of the doomed Germanwings plane in the French Alps, investigators on Tuesday resumed their grim search through debris and body parts.

Three trucks set off from the dropzone in Seynes-les-Alpes early in the morning after a hectic 48-hour road-building operation to ease access to the remote mountainside.

"It means we can work work faster, later and bring back more items," said one police officer.

Trucks now take 45 minutes to reach the base of the rocky slope where debris remains spread across some two hectares, while two helicopters hover over head to check for pieces that may have been flung further.

Somewhere in there lies the second "black box" recorder, which gathered technical data on the flight, and has yet to be found.

Search teams are having to dig into the loose earth on the assumption the black box has been buried, the policeman said.

He added they have removed "more than 4,000 pieces" of plane and human remains.

The search was expected to finish by April 8, after which a civilian clean-up group, funded by airline owner Lufthansa, will tidy up the site.

It is exactly a week since the Germanwings jet crashed into the French Alps, killing all 150 on board instantly.

Authorities believe co-pilot Andreas Lubitz deliberately locked the plane on a collision course with the mountain and are scouring his background for a possible motive.

AFP