The controversial child sex offender register has been live for a day, but there are already concerns about how stretched police numbers will check-up on offenders.

The register gives police and Corrections a central source of information to share with other government agencies, at their discretion.

Nelson lawyer Steve Zindel held an information session for local lawyers yesterday, to ensure they're up to speed on new court procedures for the register.

He said the biggest topic was the extra burden this is going to place on police and Corrections staff to ensure offenders are reporting dutifully.

"If there's changes of address or travel details, [or] if a person leaves their house for more than two days, notifications is meant to be given to Police, so that's going to be quite onerous on people and I can guarantee you people are going to forget or not do that on occasions."

Zindel said there's an Orwellian amount of information offenders must provide beyond just changes of address, like providing details of existing or new tattoos, within 72 hours of the change.

"A lot of that detail won't be provided with fulsome detail by some offenders. There's going to be a lot of checking required and a lot of under-reporting probably, and then it's only going to come to light if something goes wrong, if there'd been a lack of compliance."

Zindel said misreporting or under-reporting is likely to lead to more prosecutions, if the offender is found out.

Adults being sentenced for sex offences against children, will face a judge for both sentencing decisions and to decide whether their details are included on the register.

If they're sentenced to prison they will go on the record, and will have to provide ongoing reports on where they live, where they plan to travel, and where they're employed.

Crown and Defence lawyers will also have to submit on whether a child sex offender qualifies, even if they're not sentenced to prison, leaving it to the Judge's discretion as to whether their previous history qualifies them for the register.

Police say it's a tool for Police and Corrections staff to monitoring people who have offended, with the aim of preventing re-offending.

It's not a public register, and information is released at Police and Corrections' discretion.