Occupancy rates for motels and campsites fell 4% in August compared with the same time a year ago.
Statistics New Zealand says the trend in guest nights across all types of accommodation has been falling since September 2007.
Motels were down 10% and caravan parks by 11%.
It was the third consecutive monthly decrease compared with the same period last year.
Bucking the trend were hotel guest nights, up 32,000 in August on the same month last year.
Almost all regions had fewer bookings with Otago and Northland showing the largest decreases.
Statistics New Zealand says the drop is likely to be related to a 1% decline in overseas visitor arrival numbers recorded over the past year.