The Finance Minister says the economy can't be taken for granted as new figures show lower than expected economic growth.

Gross domestic product (GDP) rose just 0.5 per cent in the March 2017 quarter, following an increase of 0.4 per cent in the December 2016 quarter, Statistics NZ said today.

That was significantly below the expectations of most economists and the Reserve Bank.

The Kiwi dollar fell after the news against the greenback by 0.25 per cent.

Finance Minister Steven Joyce said now is not the the time to rest on our laurels or consider policies that would damage growth in key sectors of the economy.

"The fact that we've had moderate GDP growth now for the last six months, is a reminder to everyone not to take the New Zealand economic performance for granted.

"It is still a challenging international environment," said Mr Joyce.

Today's figure takes the annual growth rate to 2.5 per cent.

In a Reuters poll of 11 economists, the median forecast was that GDP grew 0.7 per cent in the quarter.

Agriculture grew 4.3 per cent due to higher milk production. This flowed through to higher dairy product manufacturing, which contributed to the overall rise in food, beverage, and tobacco product manufacturing.

Dairy exports fell 11 per cent in the March 2017 quarter, resulting in a build-up in dairy inventories.

Construction fell 2.1 per cent, with all building sectors showing a fall. Non-residential building construction, declining from a recent peak, was the key driver. This was also reflected with falling investment in both residential and non-residential building construction.

But ASB senior economist Jane Turner correctly picked growth of 0.5 per cent for the first three months of the year.

Following a surprisingly weak fourth quarter of 2016, that would suggest an economy performing well below expectations, she said.

"Growth of less than 1 per cent over six months does not fit with robust business confidence surveys," she said. "The NZ economy is supposed to be humming on the back of strong population growth, improving export incomes and low interest rates ... sub-trend growth could be an early warning that the economy is not firing on all cylinders."

In its May Monetary Policy Statement, the Reserve Bank forecast quarterly growth of 0.9 per cent.

Westpac senior economist Satish Ranchhod noted that while "some downside surprises in the March quarter may bounce back over the next quarter, we are still left with a picture of subdued per-capita growth in the economy."

Per-capita GDP has fallen in both of the past two quarters, he said.

On a per capita basis, GDP shrank 0.1 per cent in the quarter, following on from a 0.2 per cent contraction in December, for a 0.9 per cent annual increase.

Real gross national disposable income per capita, which measures purchasing power, shrank 0.9 per cent in the quarter, following a revised 1.8 per cent expansion in December, for an annual increase of 1.8 per cent.