The state averaged 667 people in full-time custody per day in the September quarter, down from 673 in the previous quarter.

The daily average was up by 35 compared to the September quarter of 2018.

It was up by about one fifth since calendar year 2016, when it was 555.

The prisoner growth is one reason why the state government is planning a new prison near Westbury.

The state averaged 613 males in full-time custody per day in the September quarter and 54 females.

Indigenous prisoners averaged 134, down by two from the previous quarter.

Tasmania had an imprisonment rate of 158.6 people per 100,000 adults in the September quarter.

That had risen sharply from 137.3 in 2016, but remained well below the national rate of 218.4.

Victoria and the ACT were the only jurisdictions with lower imprisonment rates than Tasmania.

The Northern Territory was an outlier, with a rate of 930.

It remained the case Tasmanian males were much more likely than Tasmanian females to be in jail.

The September quarter male imprisonment rate was 297.6 and the female rate 25.3.

Tasmania's indigenous imprisonment rate was much higher, at 758.9 per 100,000 adults.

However, it was also easily the lowest indigenous imprisonment rate in the nation.

There were 181 unsentenced prisoners in full-time custody on average on the first days of the months in the September quarter.