A hymn book used by members of the religious group known as the Two by Twos or The Truth.
Photo: Supplied

The number of historical sex charges laid against a Northland man who was part of a secretive sect has tripled since police arrested him last month.

The 79-year-old now faces 55 charges relating to six victims who were young boys at the time of the alleged offending.

The man was arrested as part of an investigation into accusations of sex offending that spanned three decades when he was part of an underground sect, the Two by Twos.

Police initially charged him with 17 indecent assault and sexual violation offences they say occurred throughout the country between 1964 and 1981, involving four victims, one of whom was aged under 12 at the time.

Police say a further 38 charges have been laid against the man relating to another two victims.

He has interim name suppression, and was due to appear in Kaikohe District Court later this month.

The man was excused from appearing in court on Tuesday due to ill health, and was remanded without plea.

The religious group known as the Two by Twos, or The Truth, is under investigation by the FBI for historical child sexual abuse.

The Christian sect had about 2500 members and 60 ministers in New Zealand, was not registered as a charity and had no official name or church buildings.

Earlier this year, its spokesperson confirmed police here were investigating at least one former minister for historical abuse, and it was aware of 14 cases of allegations against members.