Four Eritrean asylum seekers have claimed they were juveniles when they allegedly gang raped a 56-year-old woman in Germany and filmed the attack.

A woman was collecting bottles in Dessau in the northern German state of Saxony-Anhalt in August when four individuals, who experts say were at least in their 20s, approached her.

They told her that they had seen some bottles she had missed in a remote part of a disused school and attacked her when she went there, it is alleged.

Four Eritreans were later arrested but their exact age is unclear with three of them claiming they were 18 or 19 at the time of the incident and one claiming he was 21.

Age is important in the case because in Germany, defendants under the age of 21 are prosecuted according to juvenile law and receive more lenient punishments.

Four Eritrean asylum seekers have claimed they were juveniles when they allegedly gang raping a 56-year-old woman in Germany and filmed the attack

The woman had a broken beer bottle held to her neck and was warned she would be stabbed if she tried to fight back during the alleged attack which is said to have lasted about an hour.

It was reported that part of it was filmed on a mobile phone.

The woman suffered a stab wound to her cheek, skin abrasions and bruises and was hospitalised for several days.

Four Eritreans were later arrested in three different German states in September 2017 in a coordinated police action. A trial will be held in the regional court in Dessau-Rosslau.

Public prosecutor Frank Pieper made it clear the defendants had to remain in custody.

They are reportedly also uncooperative and have not commented on the allegations since being taken into custody.

According to the court, an age evaluation shows that the given information is highly unlikely to be accurate.