The number of available rental properties on the market in Perth has reached unprecedented levels, with 10,200 houses and units available for renters, new figures show.

Real Estate Institute of Western Australia (REIWA) figures show the number of properties available to rent in Perth is nearly three times above what is considered to be the long-term average.

The oversupply of available rentals is putting downward pressure on prices, with the median rent down to $395 per week for the three quarters to the end of March.

REIWA president Hayden Groves said the number of available properties available on the rental market was at a level never seen before.

"It really is quite startling," Mr Groves said.

"We are seeing rents fall, they will perhaps fall for the remainder of 2016 by a very small margin and that's mainly because our population growth has changed so dramatically.

"Tenants certainly have the rental market in their favour at the moment."

Activity remained slow across the Perth property market, with sales volumes down 40 per cent from the December quarter to the March quarter.

The $520,000 median house price for the first three months of 2016 is down 3.7 per cent from the final quarter of 2015.

But Mr Groves said part of the fall in the median house price was due to a spike of activity in the lower end of the market.

"In the March quarter we saw an increase in lower priced property transactions, properties less than $420,000 made up about 45 per cent of all property transactions in the March quarter," he said.