Police say there could be more victims of a child sex offender who taught in schools in Hawke's Bay and Wellington.

Charles Harter, 63, appeared in the Hastings District Court today on nine charges of indecent assault.

The charges relate to nine children he had contact with during his time as a music and drama teacher at Havelock North Primary School from 2012 to July this year.

Harter pleaded guilty to all nine charges today and was remanded in custody until sentencing on October 23.

Detective Sergeant Nic Clere of Hawke's Bay CIB says the investigation into Harter's offending was ongoing and it was possible there were more victims in the community who have not come forward yet to police.

Police have met with the Havelock North Primary School board of trustees and parents of children at the school to inform them of the investigation process.

Police have set up an 0800 number and email contact for parents of children who were taught by Harter.

'The investigation team has established that Mr Harter has taught many children during his 40 year teaching career in Hawke's Bay, Wellington and Masterton. While we have spoken to several children so far, there is a possibility there may be more victims that we don't yet know about.

'If parents have any concerns or questions about the investigation and/or any concerns about their children who were taught by Mr Harter, they can ring the investigation team in confidence and we will explain the investigation process with them."

Source: New Zealand Police.