Authorities have charged a man in his twenties, reportedly a football referee. (Representational)

Norwegian authorities have charged a man in his twenties, reportedly a football referee, with sexual offences involving some 300 teenage boys -- the biggest such case in the country's history, prosecutors said Tuesday.

"The case is a serious one, and it is the biggest case of sexual abuse in Norway to date," state prosecutor Guro Hansson Bull said in a statement.

The charges include rape, according to Norwegian media reports.

The man allegedly targeted boys on the internet, where he adopted female personas in chat forums and convinced the victims to engage in sexual acts, which he filmed, with promises of erotic photos in return.

According to the prosecutor's office, about 300 boys aged 13 to 16 were targeted since 2011, in Norway and other Nordic countries.

The man, identified in the media as a football referee, "admits the facts," his lawyer Gunhild Laerum told broadcaster NRK, but has yet to respond to each individual charge.

The trial will be held in 2019.