Forensic teams have isolated 78 distinct DNA strands from body parts recovered from the Germanwings crash site in the French Alps, one of the lead investigators says.

Prosecutor Brice Robin added that an access road was being built for all-terrain vehicles to reach the site where 150 people died.

The road will help with the removal of large parts of the plane, and could be completed by Monday night, Robin said.

Investigators have faced a huge task in trying to recover bodies and search for a second "black box" at the site, which is extremely hard to access and has required specialist mountain police to accompany search teams.

"We haven't found a single body intact," said Patrick Touron, deputy director of the police's criminal research institute.

He said the difficulty of the recovery mission was "unprecedented".

"We have slopes of 40 to 60 degrees, falling rocks, and ground that tends to crumble," said Touron.

"Some things have to be done by abseiling."

Helicopters have been going back and forth to the nearby town of Seynes - around 60 trips a day.

"Since safety is key, the recovery process is a bit slow, which is a great regret," Touron said.

Most body parts were being winched up to helicopters before being transported to a lab in the nearby town of Seynes where a 50-strong team of forensic doctors and dentists and police identification specialists is working.

Between 400 and 600 body parts were currently being examined, Touron said.

The Germanwings flight crashed on Tuesday, with French officials saying the plane's voice recorder indicates that Andreas Lubitz, 27, locked the captain out of the cockpit of the Germanwings jet and steered Flight 4U 9525 into the mountainside.