No one in the country has received a third strike.
Sensible Sentencing Trust Tauranga spokesman Ken Evans said first warnings had been increasing locally since 2010, doubling between 2011 and 2013.
This year's 39 first warnings are likely to fall short of last year's total of 77, however Mr Evans said the rate could rise during the "silly season".
He said the increasing number of first warnings was a concern.
"It certainly would be good to see that coming down. It seems people who commit these crimes need a real shake up."
However, the very low number of second warnings suggested the system was working because most people who received first strikes for committing very serious crimes hadn't been caught committing those serious crimes again, he said.
Crime had dropped dramatically locally as well as nationally since the "three strikes" legislation came in, Mr Evans said.
The Sensible Sentencing Trust claimed 100 per cent of New Zealand's strike offenders had numerous prior convictions as adults for serious offending.
Mr Evans said 38 per cent of strike offenders committed their first strike while on bail, on parole or still otherwise subject to sentence and 67 per cent committed their second strike under the same circumstances.
A Ministry of Justice spokesperson said the ministry was unable to confirm these claims.
"The first statement that 100 per cent of strike offenders had numerous prior convictions seems unlikely to be accurate as many offenders convicted of their first strike offence had no previous convictions.
"The effects of the three-strikes legislation were expected to be measured over a very long period of time. As no one has received a third strike it is too early to assess its full effects." Additional reporting, Sandra Conchie
