Statistics from the Crime Snapshot show there were 21,459 crimes committed in Christchurch last year - 3132 less than the 24,591 in 2019.
The only crime that showed an increase in 2020 was assault. There were 1895 assaults last year, compared to 1777 in 2019.
"The increase in assaults from 2019 to 2020 is relatively low and is therefore unlikely to be attributable to a single factor," said Senior Sergeant Roy Appley.
"It is possible that a rise in family harm reports has contributed to this - both as a result of Covid-related restrictions and the Integrated Safety Response work carried out by Canterbury police.
"Increased reporting, particularly of family harm incidents, is a positive thing and demonstrates increased confidence in police."
Every other crime listed in the Crime Snapshot decreased.
There were 5609 burglaries, compared to 7061 in 2019. Thefts were down from 15,197 to 13,508 and robberies decreased from 299 to 214.
Sexual assaults were also down. A total of 222 occurred, 15 less than last year, and there were 11 abductions, compared to 20 last year.
"The decrease in other crime datasets is relatively low and therefore it is difficult to accurately pinpoint a cause," Appley said.
"In the last 12 months, Canterbury district has had an increased focus on prevention activity and it is possible this has contributed.
"A Metro Targeting Team has been introduced, predominantly focused on reducing burglaries.
"There has also been increased resources dedicated to the Precision Targeting Team and the Offender Prevention Team, aimed at prevention activities with recidivist and high risk offenders."
Christchurch's crime statistics followed the national trend, which saw 268,386 crimes committed throughout the country last year - 10,468 fewer than 2019.
Assaults also increased in New Zealand by 7561, a rise of 14.1 per cent compared to 2019.
There were 9654 fewer thefts and 8033 fewer burglaries nationwide.
Christchurch crime in 2020 compared to 2019:
Assault
2019: 1777
2020: 1895
Sexual assault
2019: 237
2020: 222
Abduction
2019: 20
2020: 11
Robbery
2019: 299
2020: 214
Burglary
2019: 7061
2020: 5609
Theft
2019: 15,197
2020: 13,508
Total crimes
2019: 24,591
2020: 21,459
