SALES of second-hand homes in Shanghai climbed in May amid steadily recovering sentiment among buyers, but the growth probably won't be sustainable due to inadequate supply while the traditional slack season for property sales is also approaching.

Sales of pre-owned homes rose 3.7 percent last month to 20,758 units across the city, Shanghai Deovolente Realty Co said in a latest report.

By price, the average cost for an existing house jumped 4.7 percent from a month earlier to 18,009 yuan (US$2,904) per square meter, a record in the city, Deovolente data showed.

"Months after the central government announcement of a 20-percent capital gains tax on property sales, the local authority hasn't really implemented the policy and many home-seekers just decided to proceed their home purchase plans instead of further waiting," said Lu Qilin, a research director at Deovolente. "However, as supply remains inadequate after an extremely hectic March, coupled with other factors such as more owners started to raise their prices after seeing robust requests from home seekers and the summer is also coming, we expect more buyers to sit on the sideline."

A separate research released by Century 21 China Real Estate, one of the city's biggest estate chains, found that large-sized houses registered bigger price growth than their medium or small-sized counterparts and high-end homes also saw faster price growth.

For instance, among the city's Top 10 residential projects which recorded the biggest month-on-month price growth in May, eight cost more than 40,000 yuan a square meter and four cost more than 60,000 yuan per square meter, according to Century 21, which tracks prices at 40 major residential developments around the city.