Singapore shares were down for a second straight session by midday on Thursday, in line with other Asian bourses as soaring borrowing costs in Spain and Italy added to growing fears over the euro zone's debt crisis.

By 0522 GMT, the benchmark Straits Times Index (STI) was 0.6 percent lower at 2,767.92 points. The index has fallen about 7 percent in May alone, compared with an 11 percent drop in the MSCI Asia Pacific Ex-Japan Index.

The STI has risen about 4.6 percent so far this year, the best performers to date being developer Hongkong Land Holdings , which surged 28.5 percent, and Sembcorp Industries Ltd, which rose around 24 percent.

Among the worst losers are palm oil firm Wilmar International Ltd, which fell 25.5 percent, and commodity firm Olam International Ltd, which plunged 21.4 percent.

"While waiting for the second Greek elections to take place and for clarity on what's happening in the Spanish banking system, we're likely to see pressures on the downside on risk assets," said Jason Hughes, head of premium client management at IG Markets.

Hughes said the STI could fall below 2,500 if the euro zone's sovereign debt crisis worsens, but saw bargains in certain banking stocks such as DBS Group Holdings.

1322 (0522 GMT)

(Reporting by Charmian Kok in Singapore; charmian.kok@thomsonreuters.com)