Approvals have almost halved this month, but that is a usual seasonal change, as people take holidays instead of buying houses. In the week to January 11, 4971 approvals worth $738 million were made.
In December, house prices struck a record median price of $389,000, up 9.6 per cent on the same month in 2011, according to figures from the Real Estate Institute.
The Auckland median price was up 10.5 per cent to $535,000.
Institute CEO Helen O'Sullivan said many of the mortgages would be refinanced loans.
The Reserve Bank's figures include the refinancing of other banks' customers, any loan where the security changes and any loan where the liability holder changes.
"Interest rates are good at the moment," Ms O'Sullivan said, "so for some people, it might be an opportunity to refinance their existing mortgage and get some competition between their current provider and another provider."
Other recent figures from the Reserve Bank showed that holders of floating mortgages could save more than $700 million this year by switching to a two-year fixed rate.
A total of 916,142 floating mortgages were recorded, paying an average of 5.79 per cent a year in interest.
But those who fixed their mortgages for two years saw their rates drop to an average of 5.29 per cent, according to the statistics.
Ms O'Sullivan said the increase in mortgages could be due to the massive rise in auctions - up 68 per cent over the year, with sales by auction growing by 87 per cent in Auckland.
More people would be getting their credit sorted before going house shopping, she said.
Auckland's booming housing market spurred Finance Minister Bill English to declare Auckland Council needed to free up more land so affordable homes could be built.
"Over the next couple of years there will be thousands more houses built in Auckland ... We will need the assistance of the Auckland Council to cut through the red tape to make sure the lower-value houses get built."
Major Campbell Roberts of the Salvation Army said this week that housing was New Zealand's most urgent problem because it affected economic growth and the social wellbeing of communities.
Labour leader David Shearer said a capital gains tax was absolutely necessary to reduce property speculation. His party's policy of constructing 100,000 houses a year at an average $300,000 each was plausible because building on that scale would bring costs down 30 per cent to 40 per cent, he said.
New Zealand Federation of Family Budgeting Services chief executive Raewyn Fox said for those taking on a new mortgage, it was important to start putting money aside for any extra costs that came with a house.
"Often people have come from flatting, so often don't know much about power, water and rates. Also, it's good to have money aside in case you need to fix something."
Ms Fox also said that if a home owner ran into financial trouble, it was vital they let their mortgage provider know as soon as possible - while they were up to date with payments and not in the red - so other arrangements could be made.
Read more: Home sales need a 'sunny' side
