An analysis of traffic flows in June suggests the economy expanded at a slower pace in the second quarter.
ANZ Bank's Truckometer measures traffic flows on certain roads and calculates the economic impact.
The heavy traffic index, which is an indicator of how the economy was performing in June, dropped 0.8 percent in the month after slipping 2.1 percent in May.
The light traffic index, which predicts growth six months ahead, fell 0.7 percent in June - the first drop in four months.
ANZ Bank economist Steve Edwards said the index showed economic growth probably slowed in the second quarter from the previous one.
"We've seen a decline in the month of June. It's the first time we've seen a decline in both the light traffic index and the heavy traffic index ... since about November last year," Mr Edwards said.
"So it's indicating that there will be growth in the economy but it won't be as strong as what we've seen in the March quarter."