The housing affordability crisis has worsened with a new report showing rents have soared by as much as 25 per cent in the past 12 months.

An undersupply of housing and high mortgage rates have contributed to the deterioration in conditions for renters.
The Australian Property Monitors (APM) June quarter rental survey shows double-digit rent increases in most of the major cities in the past 12 months, with the biggest rises in Perth and Sydney.

Units in Perth soared by 25 per cent in the year to June to a median $350 a week, while in Sydney they jumped 11 per cent to $400 a week.

A house to rent in Sydney now costs a median $420 per week after an increase of 15 per cent in the past year, while median house rents in Perth increased 17 per cent to $350 per week.

Sydney is the most expensive capital city in which to rent a unit, while Darwin ($450) is the most expensive in which to rent a house.

The cheapest capital city in which to rent either a house or unit is Hobart, at $285 and $235 respectively.

APM general manager Michael McNamara said rising rents are being driven by high mortgage rates.

"On one hand landlords are trying to offset increased costs and on the other hand high interest rates deter renters from making the shift into home ownership," Mr McNamara said.