"No one like selling their house at a loss," Mr Tremain said.
"People can now sell their property, make some money, pay the fees and everyone's happy.
How high it goes, nobody knows.
The sales-volume increase was unusual going into winter, traditionally a quiet time for the market, "but it is on the back of market momentum".
Median price increases were sure to follow.
The Hastings median price rise, which went from $307,500 in April to $320,000 in May, was due to increased sales in Havelock North, he said.
The Napier median price fell from $340,000 in April to $292,500 in May as volume increased from 91 to 110.
He said the Hawke's Bay median price for March was $135,000 in 2001, $278,000 in 2006 and $275,000 in 2015 before increasing to $305,000 in April.
"It has come back in May to $290,000 but it is still showing good increase - what is March 2018 going to be?"
The gap between Auckland and Hawke's Bay prices would surely narrow, he said.
Auckland's median sale price rose to $749,000 on a 23 per cent sales volume increase in May, up $124,000 on May 2014 and 4 per cent from April.
The Auckland market has lifted the national median price 7 per cent in the last 12 months to $460,000 last month, up $30,000 on May last year and 1.1 per cent ($5000) from April.
Property Brokers Hawke's Bay manager Paul Whitaker said that as sales volumes rose so would prices.
The market was given extra impetus by the Reserve Bank cutting interest rates yesterday, which increased buyer demand, Mr Whitaker said.
While the median Hawke's Bay price fell in May, the average price rose, he said.
Colleen Milne REINZ chief executive, said the Hawke's Bay market now had a greater number of first-home buyers and investors active in the market.
Increasingly, they were from outside the Bay region.
"The Reserve Bank's introduction of the 30 per cent LVR for Auckland may have the effect of moving investors' attention from Auckland to the regions," she said.
Properties for sale in Hawke's Bay attracted the greatest increased levels of interest from Aucklanders searching on realestate.co.nz in May, up 152 per cent on the corresponding period last year.
Ms Milne said Hawke's Bay listings remained tight and vendor expectations were increasing.
Mr Whitaker said his company was experiencing more multiple offers and prices were lifting accordingly.
"There is not a lot of stock but there is the same number of buyers, if not more.
"We are in a far better market than we were a year ago for people selling their property."
House buyers were advised to "get your ducks in a row and make a decision quick".
