"This is consistent with what we've seen in previous months, with the fall in net migration being driven more by increases in migrant departures than decreases in migrant arrivals."
Meanwhile trend of more kiwi's departing for Australia - which re-emerged in July - continued in August.
Migrant departures for New Zealand citizens were up 600 for the year ended August 2018, to 34,200. Of these, 20,900 were to Australia.
This increase in departures was accompanied by a fall in the number of citizens returning to New Zealand from Australia, which led to a net outflow of 1,200 migrants.
"New Zealand's net migration with Australia is typically negative so dropping below zero is not unusual." Theyers said.
"Historically, New Zealand citizen departures have been much higher. For example, in 2012 there were 48,700 New Zealand citizens who departed to Australia, which led to a net migrant loss of 40,000."
Westpac's Ranchhod noted another factor weighing on migration "is departures of non-New Zealand citizens to areas other than Australia, which are continuing to trend higher."
Longer term he said he expected net migration would continue to gently ease over the next few years.