Net overseas migration continued its downward movement to the end of March 2010, according to preliminary data released today by the Australian Bureau of Statistics (ABS).

The figures come days after Treasury has flatly rejected Julia Gillard's election campaign call for a population growth slowdown.

ABS data shows the preliminary net overseas migration estimate (61,800 people) for the March quarter 2010 was 37 per cent lower than the historical high recorded for March quarter 2009 (98,100 people).

Australia's population reached 22,272,000 by the end of March 2010, with an increase of 403,100 people over the year. Net overseas migration accounted for 60 per cent of this growth, with the remaining 40 per cent due to natural increase (births minus deaths). The population growth rate was 1.8 per cent, down from its peak of 2.2 per cent in March 2009.

Based on preliminary figures, there were 303,500 births registered in the year ending March 2010, 3.1 per cent more than the previous year. The number of deaths registered over the same period was 141,800, 1.1 per cent lower than the previous year.

Western Australia continued to record the fastest population growth rate at 2.3 per cent, followed by Queensland (2.2 per cent), Victoria (2 per cent), the Northern Territory (1.9 per cent), the Australian Capital Territory (1.8 per cent), New South Wales (1.6 per cent), South Australia (1.3 per cent) and Tasmania (0.9 per cent).

Last week, Treasury has told the Prime Minister that rapid population growth is both inevitable and a key part of Australia's adjustment to the resources boom.

Its brief to the incoming government, released on Friday under a Freedom of Information request, warned that the nation's prosperity faced some big risks from the world economy.

The department defended its 36 million population estimate, saying it allowed for a big fall in net migration. If migration were slashed to 60,000 people a year, a third of the level it believes is likely, the population would still reach 29 million.