Singapore shares pared earlier gains at midday, weighed by worries of a messy Greek exit from the euro zone and after Chinese data showed persistent weakness in its economy.

The benchmark Straits Times Index was up 0.03 percent 2,781.33 points, down from its intraday high of 2,791.32.

European Union leaders at an informal meeting on Wednesday said they wanted Greece to stay in the euro zone while respecting commitments it had made in return for its bailout. But the leaders have been advised by senior officials to prepare contingency plans in case Greece exits.

China's HSBC Flash Purchasing Managers Index, an indicator of the country's industrial activity, retreated to 48.7 in May from 49.3 in April.

"The weakness in today's market is a result of a confluence of factors. Some people think the PMI is a real worry," said Carey Wong, investment analyst at OCBC Investment Research.

"We've been talking to a few manufacturing companies and capacity is idle. There's definitely a risk that demand may not be there," he added, which may weigh on the rest of Asia, including export-dependent countries like Singapore.

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1245 (0445 GMT)

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