More migration to Hawke's Bay, mainly from Auckland, meant more people were looking to rent and that put pressure on rental stock.
Mr Whitaker said there was a slight shortage of good properties available to rent in the area, though that shortage was not as severe as in other parts of the country.
He said Hawke's Bay had not yet experienced a surge of investors coming into the market.
"When that happens, then obviously the demand will decrease," he said.
Aucklanders coming to town would contribute to that surge, which would help ease rents.
The median rent for a unit in Hawke's Bay increased 1 per cent to $232.50, Trade Me said.
Townhouse rents increased 9 per cent to $320 and apartment rents dropped 3 per cent to $290.
A property renter in Auckland can now expect to pay at least $400 per week regardless of property size or type, Trade Me said.
Head of Trade Me Property Nigel Jeffries said that even the smallest unit or one-bedroom home would cost a typical Auckland renter $400 per week.
Outside Auckland median asking rent remained relatively stable for the fourth month in a row, up 3 per cent to $360 per week.
During the past five years, the median asking rent for a property outside Auckland has increased 20 per cent, from $300 per week in August 2010 to $360 per week in August 2015.
Median asking rents increased in 10 regions, fell in three regions and were unchanged in two regions.
The Trade Me Property Rental Price Index measures trends in median weekly rents for residential properties on Trade Me Property rented out by real estate property managers and private landlords during the past month.
About 11,000 rental properties are let via Trade Me Property each month.
