Police can now collect DNA at the same time as they take fingerprints after legislation passed in October last year came into effect on Monday.
The Criminal Investigations (Bodily Samples) Amendment Act allows police to take DNA at arrest. Previously, it could be taken only after conviction.
Justice Minister Simon Power says the law also widens the range of offences for which DNA can be taken. These include offences punishable by more than seven years' imprisonment and those related to more serious crimes such as sexual offending.
From the middle of next year, police will be able to take DNA samples for all imprisonable offences.
Mr Power says police expect to take about 4000 more samples this year and another 5000 more next year.
The DNA databank holds about 110,000 DNA profiles, including more than 8,000 unidentified profiles from crime scenes.