National Party leader Simon Bridges says "serious harm" crimes before the courts, such as rape, sexual assault, murder and manslaughter, have increased by 25 percent since the 2017 election.
However, government and police figures from February show a 2.7 drop - about 7000 - in the number of victims of crime reported for the year to January. The statistics do show a 4.8 percent increase in total number of serious assaults.
Mr Bridges said the government was more focused on reducing prison numbers than reducing serious crime, and that was hurting communities.
He said the government was not doing its job properly, and his party was "tough on crime" and "put victims at the heart of our criminal justice system".
Mr Bridges told Morning Report his figures came from district courts via written questions to Justice Minister Andrew Little.
He said there were likely a number of reasons for the increase, including people being sent back from Australia and an escalation in gang tensions.
Mr Bridges pointed to the latest New Zealand Crime and Victims Survey that found of those who were victims of crime, 77 percent did not report the offence to police.
"The media reporting around gang tensions, shootings, meth crime that flows onto other serious crime, seems much higher than it has been."
It was possible that other factors were at play, such as court cases taking longer, but he would be surprised if police or Justice Ministers disputed that crime was up, Mr Bridges said.
The New Zealand Crime and Victims Survey found 2 percent of the population experience 40 percent of crimes - and that young people, Māori and those with mental health issues were more likely to be victims.