"There were just under 20,000 sexual assault victims recorded by police during 2013, an increase of 8 per cent on the previous year, and the highest number of reports we've seen in the last four years," William Milne from the ABS said.

Reports of sexual assault in the ACT jumped more than 4 per cent in 2013 to 212, but that was fewer than the reported 220 assaults in 2011.

The statistics show nationally four in five sexual assault victims were female. More than half were aged 19 or under.

In the ACT, 55 per cent were aged under 19. More than 80 per cent of male victims of sexual assault were aged under 14. Women aged 20 to 44 accounted for 40 per cent of sexual assault victims in 2013.

The ACT did, however, have the second lowest rate of victimisation for sexual assault in the country, at just over 55 people per 100,000. Tasmania had the lowest at 35, compared to the national rate of 86.

Figures show blackmail or extortion was the only other offence to increase nationally between 2012 and 2013, although in the ACT there were no cases in 2013 compared to 2012.

Robbery, unlawful entry with intent and motor vehicle theft have all fallen to a four-year low nationally, and homicides and kidnappings also fell.

Reports of robberies in the ACT fell 31 per cent in 2013 from the previous year, continuing a steady downward trend in the Territory since 2010. Also for the first time in four years, unarmed robberies (81) outnumbered armed robberies (66).

Nationally, nearly half of all robberies involved a weapon. A knife was used in just over one in five and a gun in less than one in 10. Robbery was most likely to occur on a street or footpath.

Motor vehicle theft in the ACT dropped 30 per cent in 2013 and less than half the number in 2010.