Hobart has stretched its unenviable lead as the most expensive capital city in Australia to rent, according to a national snapshot.

The latest Rental Affordability Index has found households earning a moderate income in the southernmost capital spend 32 per cent of their income on rent.

Housing policy expert from SGS Planning and Economics, Ellen Witte, said the city was in the midst of a "housing crisis".

"We have all this population growth coming in and no real growth in housing, which is pushing up the prices," she told AAP.

"We've now seen three years in a row of rent increasing by 10 per cent per annum, which is extremely high.

"I mean, nobody's income keeps track with that in most circumstances."

Booming tourism and an increase in short-term rentals including Airbnb is placing growing strain on the housing market, Ms Witte added.

The report, released on Wednesday, rated Hobart's rental affordability at 93 on its metric, below a critical threshold of 100 for the first time.

This means an average income household in the city paying the current median rent would be under financial stress and potentially have to forgo food and bills to make ends meet.

The median rental household in Greater Hobart has a gross income of $64,500, the lowest of all capitals, the report said.

Ms Witte has called on the state government to considering restricting short-term rentals to open up more of the market.

Elsewhere, Adelaide overtook Sydney as the second least affordable capital city, while the situation remains dire for Newstart recipients across the country.

The most-affordable capital for a single person on the $18,122-a-year allowance is Adelaide but they must still spend at least 77 per cent of their earnings on rent.

That figure balloons to an impossible 135 per cent in Greater Sydney.

"The evidence is utterly compelling, the deeply inadequate Newstart rate is a driver of homelessness," Director of not-for-profit charity, Brotherhood of St Laurence, Conny Lenneberg said.

The rental index is published by National Shelter, Community Sector Banking, the Brotherhood of St Laurence and SGS Economics and Planning.

Hobart overtook Sydney last year as the most unaffordable capital.

Rental data was not sourced for the Northern Territory.

PERCENTAGE OF HOUSEHOLD INCOME SPENT ON RENT

(figures from the November 2018 report in brackets)

* Hobart - 32 per cent (30)

* Adelaide - 27 (26)

* Sydney - 25 (27)

* Brisbane - 24 (24)

* Melbourne 23 (24)

* ACT 23 (24)

* Perth 21 (21)

Source: Rental Affordability Index, November 2019