About a quarter of all residential properties sold in Sydney in the past year would have attracted the full stamp duty benefit promised to first home buyers by the Berejiklian government, while about 40 per cent would have attracted some concession, an analysis shows.

With the median Sydney house price hovering above $1 million, the highest of any Australian capital city, first home buyers will still likely need to look beyond the city to take full advantage of government's new housing affordability package, according to property analysis firm CoreLogic.

Under the new policy, announced on Thursday, first home buyers will be exempt from paying stamp duty for new and established housing with a price tag under $650,000, and would be entitled to sliding discounts up to $800,000.

While 45 per cent of properties sold in NSW last year were under $650,000, the availability of similar properties declined sharply to 26 per cent inside the Sydney metropolitan area, the data showed.