Official cash rate rises were also likely to be a factor, she said.
"Commentary from real estate agents around the country indicates that first-home buyers are an even scarcer commodity than they were in October and November last year."
Those buying at the top end of the market weren't feeling the pinch because the number of house sales worth more than $1 million had risen.
The $1 million-plus market represented 431 sales last month, 7.6 per cent of total sales, compared with 5.3 per cent in April last year.
House prices continued to rise. April's national median house price was $432,250, an increase of 10.7 per cent on April 2013.
The highest increase was in Northland where the median price had risen 16.8 per cent.
Auckland's median house price was $611,000 in April, down from $637,000 in March, but up 10 per cent from $555,000 in April last year.
The median price for homes in Canterbury/Westland was up 11.9 per cent to $395,000. The only regions where prices dropped compared with last year were Hawkes Bay (2.89 per cent), Manawatu/Wanganui (2.4 per cent), Otago (1.43 per cent), and Southland (2.58 per cent).
An ASB housing confidence survey found 48 per cent of respondents expected prices to keep rising in the next year - just below expectations at the same time last year.
ASB chief economist Nick Tuffley said the market remained tight, with listings at an extremely low level.
Sentiment about buying has improved slightly, with a net 4 per cent saying it's a bad time to buy.
