States with booming capital city property markets have seen a massive increase in youth homelessness in the last decade, new ABS Census data shows.

Homelessness among 19-24 year olds in New South Wales has more than doubled while in Victoria it's gone up 66 per cent and in Tasmania 71 per cent.

Homelessness among 19-24 year olds, 2006 to 2016, percentage increase:

NSW up 117%

Vic up 66%

Qld up 13%

SA up 23%

WA up 2%

Tas up 71%

NT down 15%

ACT up 64%

Aust. total up 46%

So what's causing this spectacular increase? You may not be surprised to hear that homelessness experts are blaming the cost of housing.

As a rough guide (the dates are not quite the same as the homelessness data), compare the figures above with the increase in cost of housing.

Mean price of residential dwellings, Sep 2011 to Sep 2017, percentage increase:

NSW up 65%

Vic up 44%

Qld up 17%

SA up 17%

WA up 0%

Tas up 21%

NT down 16%

ACT up 22%

Aust. total up 39%

The national peak body for homelessness in Australia, Homelessness Australia, pointed to the increased cost of housing. It called for a reform of the taxation system that "encourages investors to own many properties while thousands don't have a roof over their heads."

The St Vincent de Paul Society also pointed to housing prices. CEO Jack de Groot said many have been "cut off" from the prosperity of the state's growing economy.

The Society also called for government action on the housing affordability crisis.

'We need more social housing'

As the cost of housing has increased, the proportion of housing set aside for the most vulnerable - social housing - has been going down. According to Homelessness Australia, there are 200,000 Australians waiting for social housing and homeless agencies are turning away 250 people every day because of the lack of social housing.

RMIT University Professor of Housing and Homelessness Guy Johnson said rising housing costs are leaving many Australians at risk of becoming lifelong renters.

"This places a large proportion of the population in unstable housing, leaving them vulnerable to health and financial shocks," he said.

When those shocks come, they may join the long queue for social housing.

Aside from the increase in the number of homeless people, the rate of homelessness in the broader population of young people has also gone up - from about 62 per 10,000 people to about 72 per 10,000 people.

Two-in-five of those who are homeless are under 25.

The rate of increase of homelessness among young people was higher than among the broader population. In NSW, for example, where the number of homeless 19-24 years old went up by 117 per cent, the figure went up by 70 per cent among the broader population (which is still pretty bad).

The Census results come 10 years after Rudd Government made a commitment to halve homelessness by 2020, which is two years away. The national rate of homelessness including all ages has gone up by about 14 per cent since 2006.