Could the tides crossing the Tasman be turning? In April, for the first time in more than two decades, more Australians relocated to New Zealand to live than vice versa.

The most recent permanent and long-term migration figuresfrom Statistics New Zealand show a net monthly inflow of 100 migrants from Australia to New Zealand in April 2015 – the first time since 1991 there have been more Australians arriving in New Zealand than New Zealanders going to Australia. The net figures account for people arriving to live in New Zealand from other countries as well as New Zealanders departing for overseas, and have been seasonally adjusted.

The number of New Zealanders crossing the Tasman has dropped by more than half in the past two years – from 45,700 in the year to April 2013 to 22,300 in the year to April 2015. Statistics New Zealand reported a net annual loss of 1,900 people in the year to April 2015 – the smallest figure since 1992 and well down from 11,100 in the same period in 2014 and 34,100 in 2013.

Since Statistics New Zealand’s series began in 1982, the highest ever net inflow it recorded from Australia was 400 migrants in the year to both July and August 1983.

The flow between the two countries can change in scale and direction very quickly, according to the independent research body the Royal Society of New Zealand, given New Zealand’s large expatriate population and Australians’ unrestricted access to the New Zealand labour market and welfare entitlements. New Zealanders’ entitlement to Australian welfare was significantly curtailed by the Howard government in 2001.

The Royal Society last year estimated that there were 650,000 New Zealanders living in Australia. But though many New Zealanders do tend to spend periods overseas, many eventually return. In the year ending March 2014, just over 27,300 citizens returned home after 12 months or more overseas – the largest number since the 12 months to March 1991.

Net migration to New Zealand has been mostly increasing in recent years, which Statistics New Zealand attributes mainly to fewer citizens leaving for Australia as well as more people arriving from other countries.

New Zealand’s economy is performing strongly, while the Australian economy is at the end of a mining boom. Mining investment is falling and the rest of the economy is “so-so”, according to HSBC economist Paul Bloxham.

The population of New Zealand was recorded as 4.4m in June last year, and the country has been gaining around 4,500 migrants every month for the past six months. Unadjusted figures showed a record net gain of 56,800 migrants in the year to April 2015 – an increase of slightly more than 65% on the previous year’s 34,400 people. Migrant arrivals for the year had increased by 16%, while departures decreased by 11%.

The countries with most migration to New Zealand in the 12 months to April were India (12,200), China (7,800), the United Kingdom (4,600) and the Philippines (4,000).