Growth in New Zealand's house prices accelerated for a fourth consecutive month in April, driven by the country's biggest city, the government property valuer said. Quotable Value's residential property price index rose 8.4 per cent in the year to April 30, compared with an annual rate of 7.7 per cent in March. The index is now 22.4 per cent above the market's previous peak in late 2007. "The steepening of the national index is indicative of the sharp rise in Auckland values over the past six months," Quotable Value spokeswoman Andrea Rush said. House prices in the Auckland region, where there is a significant housing shortage, were 14.6 per cent higher in the year to April compared with a 13.9 per cent rise the month before. Rush said record high immigration would sustain values in Auckland where demand outstrips supply. Prices growth in earthquake-damaged Christchurch slowed to 4.7 per cent over the past 12 months against 5.3 per cent the month before. The Reserve Bank of New Zealand has said it is concerned the housing market is heating up again. It is expected to tighten rules covering lending to residential property investors, seen as one of the drivers of the Auckland market, which may increase their cost of borrowing.