HONG KONG, May 21 (Reuters) - Hong Kong shares ended lower for a fourth straight session on Monday in dismal turnover, dragged down by weakness in HSBC Holdings Plc, Europe's largest bank, as investors await details of a pledge by global leaders over the weekend to keep Greece in the euro zone.

The Hang Seng Index finished down 0.16 percent at 18,922.32. The China Enterprises Index of top mainland listings in Hong Kong ended up 0.06 percent at 9,582.46.

The CSI300 Index finished up 0.51 percent at 2,587.23, powered by strength in the rail sector after the railway ministry announced over the weekend that it would decentralise bidding for railway projects, aiming to increasing transparency.

HIGHLIGHTS:

* Technical resistance for the Hang Seng benchmark is seen at 18,985.4, the lower end of a gap that opened up on the charts between May 17 and 18 - a level that could be overcome with a significant development in Europe. Markets in Hong Kong remain vulnerable to a short squeeze after short-selling interest averaged 11.2 percent of total turnover last week.

* Hong Kong bourse turnover hovered near a four-month low, about 13 percent below its 20-day moving average.

* In a sign that Europe remains the most significant risk factor, HSBC sank 1 percent to a four-month closing low and was the top drag on the Hang Seng Index. It has lost 10.7 percent this month, but bounced off the session's low at HK$62.55.

* Tencent Holdings Ltd slumped 3.4 percent as funds continued to exit one of the top performers this year. Tencent has lost 12 percent after ending at HK$246.80 on May 3, an all-time closing high. (Reporting by Clement Tan; Editing by Chris Lewis)