Homelessness in the South has reached "crisis" levels, the National Housing Federation (NHF) has warned.
The amount of homeless people in the South is soaring
New figures reveal Portsmouth has the fourth highest number of homeless families in the South East.
The city has nearly 9,000 households on its housing register who need permanent homes, a rise of 85% since 2001.
Southampton is the fifth highest, with 8,000 households on its register. Government data, to be published next week, will confirm the problem.
Peter Simmonds, from the NHF, described the total number of families in temporary accommodation as "staggering".
He said: "Anyone can find themselves in this situation (homeless) if they suffer job loss or family breakdown.
"But what we really need across the South is an increase in more affordable housing to meet the backlog and future demand."
More than 1,400 families in Southampton and Portsmouth were placed in temporary accommodation in 2003 and 2004.
Etty McKinley, from People off the Streets, an Isle of Wight-based charity that helps find homes for families in temporary accommodation, said: "Not enough houses are being built.
"Yes, there is affordable housing, but at £100,000 a time, affordable to whom?
"One big problem is key workers who get grants to help them buy housing, and then sell the house on for a profit."
Trevor Pickup, director of the Society of St James, a charity in Southampton which provides help and accommodation for homeless people, believes more affordable housing is the long-term solution.
"On any given night we can have over 20 homeless people on the streets," he said.
"We deal with a huge range of people - men, women, young, old, some with issues such as alcohol or mental health, some with a combination of issues.
"Some have simply lost their support network, don't have friends, family or credit cards to help them out of short-term financial difficulties."