New Zealand\'s services sector is seeing its strongest sustained period of growth in four years, according to the latest performance of services index (PSI) released Monday. The BNZ-Business New Zealand PSI for May was 56.2, on a scale on which above 50 indicates expansion and below 50 contraction, and was the highest May result since 2007. The May result was identical to the April result, and followed 55.7 recorded in both March and February, representing four straight months of healthy levels of activity, said Business New Zealand chief executive Phil O\'Reilly. \"However, it is important to point out that the first few months of 2012 started out in a similar fashion, but faded during the winter months. Time will tell whether other recent and positive economic indicators for the economy will lead to further expansion in the service sector,\" O\'Reilly said in a statement. BNZ senior economist Craig Ebert said in the statement that it was the strongest sustained growth pulse from New Zealand\'s services sector since the economy began emerging from recession in 2009. All five main PSI sub-indices were in expansion in May, with new orders/business at 59.5, activity/sales at 56.9, employment at 53.6, stock/inventories at 53.7 and supplier deliveries at 56.1. The GDP-weighted BNZ-Business New Zealand Performance of Composite Index, which combines the Performance of Manufacturing Index and the PSI, for May was up 0.6 points to 56.9.