National group, Propertyology, said heavy demand and short supply would allow landlords to increase rents.

They said Orange was among regional areas where a rental boom was likely in the next couple of years.

And the head of one of Orange's leading estate agencies handling rentals has backed the forecast, tipping rents will rise by 10-20 per cent due to a lack of available properties.

The median cost of renting a three bedroom house in Orange has already risen by $10 a week to $370 this year.

Propertyology Head of Research, Simon Pressley said the boom would be felt in cities outside Sydney and Melbourne.

"Propertyology is tracking 50 individual towns across Australia with vacancy rates below one percent. It is the tightest rental conditions that Australia has ever seen," he said.

On Tuesday there were only 75 houses and units available to rent in Orange.

Occupancy rates of below one per cent have been seen in the city this year.

Mr Pressley said mum and dad investors owned most rental properties. But he said they were finding it increasingly hard to get finance to buy investment properties and therefore increase the supply for renters.

He said banks needed to process applications quicker and reduce investment loan interest rates. "It beggars belief that something which could be approved in a couple of days, 30 years ago, today takes a few weeks."

McCormack Barber Real Estate director Peter McCormack said they were already seeing rent prices rise in Orange.

"I can easily see 10-20 per cent [rises] in the next couple of years," he said.

Mr McCormack said he also expected house prices would rise by 10-20 per cent.

"We know there is an under-supply, it's simple economics," he said.

Mr McCormack said houses were selling quickly in Orange with investors having to compete with first-home buyers. "The last three homes I've sold under $500,000, there have been 100 people inspect those homes in total. Each one has sold within 48 hours," he said.

Mr McCormack said normally 10-30 per cent of potential buyers were investors but the number had dropped to below 10 per cent.

Blowes Real Estate residential sales manager Chris Tyack said they did not have any rental properties available right now.

Property groups realestate.com and domain.com this week said the median weekly rent for houses in Orange was $370 for a three-bedroom house, $320 (2br) and $450 (4br).

However they varied on median prices for units with two-bedroom being $280-$300.