A perfect storm of job losses and housing benefit cuts will increase homelessness at a time of squeezed budgets, support groups say.
Shelter Cymru warns of "problems on all fronts", while other organisations fear the worst is yet to come.
Rough Sleepers Cymru said there was already a huge spike in the number of people coming forward.
The Department for Work and Pensions said it had worked to bring fairness to a system that was "ineffective".
However, there is concern the situation will get worse when cuts to housing benefits and public sector job losses kick in.
Joy Kent, director of Cymorth Cymru which is the umbrella body for organisations helping people to find and keep their homes, said the future was "scary".
"We're already seeing an increase in demand for services and a fall in income for those services to be provided so it's a double whammy," she added.
Other groups working at the sharp end say they are seeing a big rise in people getting into difficulties.
Tim Paddock, chairman of Rough Sleepers Cymru, said: "Already we're seeing a huge increase in homeless presentations - the numbers are up massively.
"Normally we would get a little spike as we go into the cold period. It's gone up more than I've ever seen since I've been working in the homeless sector [eight years]."
The number of households classed as homeless in Wales rose 10% between June 2009 and June this year.
That rise was partly driven by an increase in people who lost accommodation that was tied to a job, or occupants who were required by a landlord to leave a rented property.
But Mr Paddock added: "The first wave [of homeless people] in the recession was people on short-term contracts and part-time employees.
"As we move on into these benefit changes, what you will see is that many vulnerable individuals are affected - people with mental health issues, or a learning disability, or a personality disorder or people who came through the care system."
Ceri Dunstan, of Shelter Cymru, said as well as redundancies, problems were also being caused by reduced working hours and people not being able to make rent or mortgage payments.
"I think we're going to see a lot more people falling into difficulties in the private rented sector - that's going to be the big concern for us," she said.
"Some of the changes being brought in [by the UK government]... if you've been on Jobseekers' Allowance for 12 months or more, your housing benefit will be cut by 10%.
"We're talking about people who are in poverty anyway and I think our opinion is that it's perverse and bizarre and we can't see what the reasoning behind that is."
Other benefit changes include an expected reduction in Local Housing Allowance payments and new limits on the amount paid according to the size of a property.
The Department for Work and Pensions said it had worked to bring fairness to a system that was "ineffective, wildly expensive and entirely unsustainable".
A spokesperson said: "Housing benefit has spiralled out of control over the last decade, costing taxpayers billions every year and plunging thousands of vulnerable people into an unbreakable cycle of benefit dependency.
"Working families should not have to pay to support a benefits system which allows people to live in properties they themselves could never afford.
"We know that many people will make up any shortfall in housing benefit, or renegotiate their rent with landlords. But we have also tripled the money available for discretionary payments, with £140m being made available over the next five years, to support those most vulnerable."
The assembly government said its new housing measure would enable local authorities to apply to suspend the right to buy council houses in areas of housing pressure.
Ministers in Wales also said they had exceeded their recent target in providing affordable homes, but admitted ambitious targets would be impossible in the current climate.
Earlier this year, Deputy Housing Minister Jocelyn Davies announced £1m of extra funding for a variety of projects to tackle homelessness.