New Zealand lost a net 850 people through migration last month - the biggest monthly outflow for 11 years - dashing hopes that March's net inflow marked a turn for the better.
Averaging April's loss with March's gain of 230 gives a net monthly outflow of 310, in line with the average monthly outflow over the past year.
Permanent arrivals dropped 15 per cent between March and April, to the lowest level since November 2005.
But average arrivals over March and April, at 7000 seasonally adjusted, were 100 more than the average over January and February.
Departures were little changed - 7280 compared with 7310 in March - most of them New Zealand citizens (5410) and most of them going to Australia (4550).
"Although the April figure probably overstates the weakness in net migration, it does suggest that the improvements we saw in February and March were a mirage," Infometrics economist Matt Nolan said.
"In the past three months, permanent arrivals have only risen 1 per cent from a year earlier," he said.
"Furthermore, even with the global economy weak, New Zealand citizens have refused to come home, with New Zealand citizen arrivals down 5.3 per cent from a year earlier."
For the year ended April New Zealand suffered a net loss of 4000 people from migration, compared with an average annual net gain of 16,500 over the previous 10 years.
Arrivals at 83,800 were up 1 per cent on the year to April 2011, but departures at 87,800 were up 13 per cent.
The net loss of people to Australia was a record 39,800 and the net loss of New Zealand citizens to Australia was 39,600.
Australia's unemployment rate is 4.9 per cent, against 6.7 per cent in New Zealand.
"With this difference likely to continue, net outflows from New Zealand are expected to persist," Nolan said.
Deutsche Bank chief economist Darren Gibbs expects "modest" net outflows to continue over the rest of the year.
"This is likely to dampen activity in the housing market in particular, especially the demand for new dwellings, at least outside Auckland," Gibbs said.
"Whilst New Zealand as a whole is losing population through net migration, this is not true of the Auckland region."
Statistics New Zealand said that 600 Christchurch residents moved overseas last month, down from 800 in April last year in the immediate aftermath of the February earthquake, but still higher than the 400 who left the country in April 2010.
Christchurch attracted 400 overseas migrants last month, unchanged from April last year but down from 500 in April 2010.