Stephens: Reserve Bank probably considering other tools

He said the data for March had shown rapid growth in house prices continued through most of the country - and the strength dramatically returned to Auckland.

Stephens said the fact that new loan restrictions and rules around capital gains had only had a temporary effect when they were introduced at the end of last year was not a surprise, but many people had been taken aback by how quickly Auckland's market had taken off again.

Real Estate Institute figures show year-on-year,  seasonally-adjusted, Auckland's median price rose by 7.7% in March to hit a new record high of $820,000. Sales volumes were also up by 66.8% on February, although they were down by 21% on March 2015.

Stephens said low mortgage rates were driving price rises, adding fire to the impact of population growth and a strong economy.