Perth's shrinking rental vacancies continued to boost rents over the first quarter of the year, according to the latest figures from Domain.

Over the quarter, rents grew by 2.7% to $375 for houses and 6.7% to $320 for units. Despite these gains, Perth remained the most affordable rental market for both housing types.

"In the space of a few years, Perth has gone from the third most expensive rental market to the most affordable of all the capital cities. This has occurred as the mining downturn, weak population growth and a flood of rental listings gave tenants the upper hand," said Nicola Powell, senior research analyst at Domain.

The growth in rents is driven by the declining vacancies in the city, providing landlords greater grounds to raise asking rents.

Separate figures from SQM Research show that in March, the vacancy rate in Perth is 1.9%, down from the previous month's 2% and a significant drop from last year's 2.9%.

"Most states and territories have seen a lift in rental listings over the second half of March as the coronavirus pandemic impacts short-term rentals and tenant hip pockets due to income reduction or loss of employment," Powell said.

However, rental price increases could stop if Perth starts manifesting signs of rising vacancies, Powell said.