There was a 42 per cent drop in robbery offences for the six-week period from mid-March compared with the previous five years, the NSW Bureau of Crime Statistics reveals.

Bureau chief executive Jackie Fitzgerald says the "huge" drop in robberies is not unusual, but she is surprised domestic violence assaults remained stable.

"It is reasonable to expect that domestic violence would increase during a lockdown period, but that hasn't shown itself to be the case," Ms Fitzgerald told AAP on Thursday.

NSW Attorney-General Mark Speakman said the results were pleasing but many victims of crime would have slipped through the cracks.

"We know that many victim-survivors of domestic and family violence are suffering behind closed doors," Mr Speakman said in a statement.

Ms Fitzgerald said the data set could potentially help explain why people commit crimes.

"People are spending much more time at home and less time in commercial premises ... and that's certainly affected their opportunity to offend and motivation to offend," she said.

The fall in non-domestic assaults was also unsurprising after people were restricted from drinking in pubs and licensed premises, Ms Fitzgerald said.

Sexual assaults were down 32 per cent and shoplifting was down 55 per cent.

The bureau examined key offences recorded by police from the time measures were put in place in NSW to control the coronavirus pandemic.

Cocaine possession was 40 per cent lower while amphetamine possession was 30 per cent higher, the report showed.

Ms Fitzgerald said more people were found with cannabis and amphetamines as a result of proactive policing while "party drugs" were likely scarce due to the lockdown.

"With the reduction in crime, police have been able to spend more time on drug detection."

The bureau plans to map crime rates as society begins the shift back to normality.

"We believe this is most likely a temporary abatement in offending rather than anything that would persist into the long term."

NSW Police Minister David Elliott said in a statement on Thursday the state government is committed to delivering an additional 1500 police officers over four years.

Australian Associated Press