OSLO, March 28 (Xinhua) -- A 40-year-old man in Norway will be charged for sexual offence against over 50 minors, public broadcaster NRK reported Thursday.

The man from Trondheim in central Norway, who has his own children, is permanently employed and has previously been convicted in three cases for keeping sexual abuse material, the report said.

This case has evolved since the accused man was first detained in December last year, police said at press conference.

The charges concern, among other things, the purchase of sex, abuse and direct video transfers from the Philippines, but also physical abuse and violent rapes.

"We have questioned 21 children under the age of 16. We have also questioned someone over 16," said Marianne Hoyer from Trondelag police district.

Most girls in this case are between 13 and 15, but some are also as young as 11 years, Hoyer added.

The charge will be extended and it could end up including more than 50 victims, she said.

"The first contact happens on Instagram. Many girls have profiles there and information about them as Snap-users. Then he has contacted the girls at Snapchat directly. Afterwards, it happens what we have warned about: Children contact someone they do not know," Hoyer said.

The accused man was arrested on Thursday morning for eight new weeks.

He consented to further detention and acknowledged essential charges, said Kolbjorn Lium, the man's lawyer.

The case reflects a major social problem, Hoyer warned.

"Children and young people must be warned against having contact with people they do not know. We think - and have experienced - that it is striking how easily girls share nude pictures and videos where they do things with themselves that are gross," she said.