REINZ chief executive Helen O'Sullivan explained the falls by saying the housing market was "highly seasonal" and prices and volumes tended to ease in January months.
"Agents across the country are reporting continuing shortages of listings and positive buyer enquiry, even after taking into account the normal slowdown in activity over the Christmas/New Year break."
See a regional breakdown of the stats here.
On a seasonally adjusted basis, January's sales volumes were typical of this time of year, O'Sullivan said.
Houses took nine days longer to sell last month compared to December but O'Sullivan said the number of days to sell has improved by six days on an annual basis.
That indicated high levels of buyer activity across the country, she said.
ASB Bank economist Jane Turner said house sales figures were "often more volatile than usual over the summer holiday period."
Using the bank's seasonal adjustment, Turner said house sales lifted 11.5 per cent in January, following a 7 per cent decline in December.
Turner said the Reserve Bank had become "increasingly nervous around housing market developments and the recent acceleration in credit demand."
Figures for December and January suggested demand remained firm, while supply was still low.
"As a result we can expect further price increases in the coming months. The RBNZ will be watching these developments closely, mindful of the risks to inflation and financial stability. We continue to expect the Reserve Bank will leave the Official Cash Rate (OCR) unchanged until March 2014 in light of the gradual pace of recovery, elevated NZ dollar and weak labour market."
There was, however, a small, but growing chance, the Reserve Bank used what are known as " macro prudential tools" later this year in order to try ease housing market pressures.
Auckland's largest real estate firm Barfoot & Thompson last week reported it sold 100 fewer properties in January compared to December and the average sale price fell by just over $23,000. State valuer Quotable Value yesterday released its stats showing house values rising 6.2 per cent over the last year and 1.5 per cent over the past quarter.
This morning's REINZ stast show Southland the only region to record a monthly increase in sales volume, up 2.5 per cent.
Taranaki recorded a new record high median price of $310,500, 10.5 per cent more than December.
There were 449 house auctions in January, nearly double the number compared to January 2012. Of all auctions around the country, 73.5 per cent were in Auckland.
