BERLIN (AFP/REUTERS) - Details emerged on Thursday about the co-pilot who French authorities say "deliberately" initiated the descent of the Germanwings flight that crashed this week, killing all 150 people on board.

The 28-year-old German, Andreas Lubitz, had worked for Germanwings, a Lufthansa subisidiary, since September 2013, a Lufthansa spokesman said Thursday.

He qualified as a pilot at the Lufthansa training centre in the northern city of Bremen and began flying for Germanwings immediately after completing the course. He had 630 hours of flight experience, she said. The Lufthansa pilot training academy in Bremen declined to talk about him.

Lubitz was from the western town of Montabaur and lived with his parents there while keeping a flat in Duesseldorf, a Germanwings hub and the city for which the doomed flight from Barcelona was bound, Montabaur mayor Gabriele Wieland told national news agency, DPA.

He was described by acquaintances in his hometown of Montabaur as a "normal guy" and "nice young man".

"He was a completely normal guy," Mr Klaus Radke, the head of the local flight club where Lubitz received his first flying licence years ago. He returned in the fall for a refresher course with Mr Radke. "I got to know him, or I should say reacquainted with him, as a very nice, fun and polite young man."

The small town of 12,000 in western Germany was in shock on Thursday at the news that French prosecutors suspect Lubitz of deliberately crashing the Airbus plane.

The German authorities were at loss to explain why the first officer for Lufthansa's budget carrier appeared to have taken sole control of the A320 airliner when the captain was out of the cockpit and slammed it into a fatal descent.

Lubitz appeared to have led an active lifestyle, running a half-marathon in a good time and showing an interest in pop music and night-clubs, according to his Facebook page, which also featured a photo of Lubitz by the Golden Gate Bridge in San Francisco.

"I'm just speechless. I don't have any explanation for this. Knowing Andreas, this is just inconceivable for me," said Mr Peter Ruecker, a long-time member of the flight club who knew Lubitz well.

"Andreas was a very nice young man who got his training here and was a member of the club," Mr Ruecker said. "He was a lot of fun, even though he was perhaps sometimes a bit quiet. He was just another boy like so many others here."

"He had a lot of friends, he wasn't a loner," he added. "He was integrated in the group. Our club is mostly made up of young people who learn how to fly gliders and then get their licence and then perhaps, like was the case with him, to make the jump into commercial aviation."

His local flight club carried a black ribbon on its website with the flight number and the name "Andreas".

Near the small, white house in the town where Lubitz lived and where the police quickly set up guard, neighbour Hans-Juergen Krause said he was "really shocked" by the news.

Mr Armin Pleiss, head teacher of the Mons-Tabor-Gymnasium high school, where Lubitz graduated in 2007, told Reuters: "I am just as shocked and surprised as you are."

Lubitz attended the school of 1,300 students before Mr Pleiss became the principal.

Germanwings has so far given only sketchy biographical details of the co-pilot.

German Interior Minister Thomas de Maiziere said on Thursday that current information suggested that Lubitz, had no links to terrorism. "According to the current state of knowledge and after comparing information that we have, he does not have a terrorist background," he said.

French prosecutor Brice Robin said Lubitz was "not known by us" to have links to terrorism or extremists, and that the German authorities are expected to provide additional information on his background and private life later on Thursday or Friday.

Lubitz was registered as a member of a private flight club, LSC Westerwald, and was an avid runner who often took part in local races, according to public records.

The captain of the two-man crew, who has not been identified, had more than 10 years of experience with German flag carrier Lufthansa and its subsidiaries and had clocked up more than 6,000 hours of flight time, most of them on Airbus planes.

The daily Bild named him only as German national Patrick S., in keeping with strict privacy laws, and said he was a father of two children.

Lufthansa said it had no plans to name the flight personnel at this stage of the investigation "to protect the crew and their families", a spokesman told AFP.