Bad weather and holidays have knocked activity in the services sector.
The BNZ - Business New Zealand Performance of Services Index fell six points to 52.8 in April, from March - the lowest level of expansion since late 2012.
A reading over 50 indicates expansion.
Activity, sales and new orders fell, while employment expanded.
Doug Steel, a BNZ senior economist, said one-off factors such as Easter and ANZAC Day were likely to blame for the result.
"We are just a little wary of what is in this April number but we do put it down to the weather and those timing of holidays, we do think the underlying momentum is better than the headline suggests here," he said.
Last week, data showed the manufacturing sector was also expanding at a slower rate.