Homeless organisations are expecting next week's national census will show an increase in the number of homeless people, as they prepare to send teams out to make sure those at the very edge of society are included in the count.

The Launch Housing program in Victoria is one of several organisations that will spend a week sending staff out to meet people on the streets, in rooming houses and caravan parks, encouraging them to be a part of the census which is conducted every five years.

According to chief executive officer Tony Keenan, the numbers are likely to show a deteriorating situation.

"We're pretty sure that there'll be a significant increase in homelessness overall. The demand on our services, all the indicators would suggest that," he said.

He said that it was not just an increase in "rough sleepers" but people who have found themselves in sub-standard, short-term living arrangements.

"We're also certain that we'll see a bigger increase in overcrowding simply because we've lost so many rooming houses, caravan parks, those options that people on the edge had, have disappeared," Mr Keenan said.

Council to Homeless Persons chief executive Jenny Smith said the collection of data was vital to providing a snapshot of the number of people in vulnerable situations.

"The red flags have been there for years," Ms Smith said.

"Since the last census, a perfect storm of ballooning housing prices, static wages and a poor employment market have lead to the homelessness crisis we're facing today."

Hidden homeless should mark their suburb as 'none'

The last census in 2011 revealed that more than 105,000 people were without a safe, permanent place to call home and another organisation, Mission Australia, was also expecting a rise in that number.

Spokesperson Catherine Yeomans said it was important that people reported their living situation correctly.

"If a person is without a home on census night, they must record their suburb as 'none'. This applies to rough sleepers as well as the hidden homeless," she said.

"The hidden homeless population includes those who might be couch surfing, living in someone's spare room or garage, staying in homeless, crisis or transitional accommodation or boarding houses or living in a severely crowded dwelling."

Homeless urged to show the need for rent caps

Mr Kenney said it was vital that homeless people demonstrated the need for cheaper housing. ( ABC News: Helen Brown )

One of those reaching out to the homeless to collect information is John Kenney, who started living occasionally on the streets when he was seven years old, and then all the time from the age of 18.

Now 61, he is settled in his own apartment, and will be working with the Council for Homeless Persons to make sure "his community" has a chance to fill out the census form.

"Some won't tell me where they live. But if I come out and live with them for a couple of nights like I do every now and then, then I'll meet them at a certain spot."

Mr Kenney has also seen the growing problem with homelessness, especially on the streets of Melbourne, and said he would encourage the people he meets to use the census to show the need for a cap on rents for those with few choices.

"I keep telling them that they need to raise up their voice and tell them that yes, I'm homeless, I want a house. I need this," he said.

"Without the count, they're not going to know where the money's going to go."

His comments were echoed by a woman living in a caravan park unit, who did not wish to be identified.

She said she would be doing the census and wanted governments to react to it or "there's no point in doing it otherwise".

"We need things like cheaper housing, shorter waiting lists for the people who need decent housing."

Action on homelessness vital

Mr Keenan said the census had become more effective and it was worth putting out trained staff to help others complete the survey.

"The only way you can talk to people who are vulnerable and on the street, and often perhaps hiding, is having people on the ground who are connected to and know the people," he said.

Ms Smith said governments must take note when the census numbers were collated.

"What we don't want is to be standing here in 2021 at the next census, looking down the barrel of a homelessness epidemic that has continued to spiral out of control," she said.

"The heavy lifting needs to be done at both the state and federal level. A cohesive strategy to tackle the housing crisis is a vital foundation for all efforts."

Recent local surveys in Melbourne and Sydney have shown a significant increase in the number of "rough sleepers".

The information from homeless people will be collected over a week, to give time to find those who do not have a regular place to call home.