Parliament has passed a bill under urgency that fixes a flaw in the Child Sex Offender Register which caused more than 100 offenders to be taken off it.

The bill passed its third reading, its final stage, by 106 votes to 14 on Tuesday night.

Deputy Prime Minister Paula Bennett introduced the bill and told MPs the register, set up in October last year, apparently didn't cover all offenders.

"There are 107 offenders who have been taken off the register who were intended to be on it," she said.

"Any retrospective law is complicated, but we've seen a problem and we're moving to fix it urgently."

Ms Bennett explained there was a problem with offenders who were convicted before the law came into effect but not sentenced.

There was also a problem with those sentenced before the law came into effect and were on release conditions.

"The 107 offenders have been monitored by police and Corrections during the time they were taken off the register, but there are certain additional conditions that they will now be subject to as a result of being placed back on the register," she said.

Questioned by opposition MPs about how soon that would happen, she said they would be back on the register within 48 hours.

The Greens were the only party voting against the bill. They opposed the register when it was established.

Under the legislation that set up the register, offenders stay on it for life, 15 years or eight years depending on their offences and the sentences imposed.

If they fail to provide required information about themselves, which includes home and work addresses, any aliases, email address and car registration number, they can be fined or sent to prison.

The register can be accessed by government agencies but not the public.