Housing lending fell in December, month-on-month, for the first since Reserve Bank records began, the central bank's latest credit data shows.

The Reserve Bank says mortgage credit fell by $50 million to $170.95 billion in December from $171 billion in November.

That's the first monthly absolute dollar decline since the Reserve Bank started collecting the data in June 1998.

Previously there had never been a month-on-month drop, with the previous low being an increase of $101 million from September to October last year.

The biggest monthly gain recorded by the Reserve Bank in housing lending was $2.2 billion in March 2007.

The fall in mortgage debt comes after the Real Estate Institute of New Zealand (REINZ) said earlier this month that house sales volumes and prices fell in December - from a weak base - compared with both December 2009 and November 2010 as the number of new sales listings dropped and demand softened.

REINZ said the volume of sales in December fell 11.3 per cent to 4397 from 4957 in December 2009 and 14.4 per cent from 5,138 in November 2010.

The national median house sale price dropped NZ$8,000 or 2.2 per cent to $352,000 in December from $360,000 in November.

However, despite the monthly fall, mortgage debt was up $3 billion, or 1.8 per cent, year-on-year in December from 167.9 billion in November 2009.

Consumer credit did, however, record a $76 million month-on-month increase rising to $11.99 billion from $11.92 billion in November. Over the year it fell by $78 million, or 0.7 per cent, from $12 billion in December 2009.

Business credit, which the Reserve Bank said in last November's Financial Stability Report that it wanted to see modestly grow to help sustain an economic recovery, rose by $1 billion to $73.04 billion in December from $72.03 billion in November.

Year-on-year business credit was down $1.4 billion, or 2 per cent, from $74.4 billion.

Meanwhile, agriculture sector debt fell by $220 million month-on-month to $47.81 billion in December from $48.03 billion in November. Year-on-year it rose $692 million, or 1.5 per cent, from $47.1 billion.