SHANGHAI (Reuters) - Mainland China stocks opened sharply lower Wednesday and were poised to snap a 10-day winning streak after officials failed to inspire confidence in stimulus plans intended to revive the economy.

As of 0132 GMT, the benchmark Shanghai Composite index fell 4.6% while the blue-chip CSI300 Index dropped more than 5%.

The A-share market comprised of stocks listed in Shanghai, Shenzhen and Beijing had a roller-coaster ride a day earlier after returning from a week-long holiday break, with turnover hitting a record 3.485 trillion yuan ($493.17 billion) on Tuesday.

Hong Kong's Hang Seng index is one of the best-performing major global markets this year, having seen its steepest rally in a generation over recent weeks. It edged up about 1% in early trading.

"The market is widely anticipating a fiscal stimulus announcement sometime this month, something like 2-3 trillion yuan is the range being talked about," said Alvin Tan, head of Asia FX strategy at RBC Capital Markets.

"The positive sentiment on China assets lately is premised on expectation of a major fiscal stimulus package, so that sentiment will turn quickly if we don't get some package at least matching the range above."

In overseas markets, Singapore-traded FTSE China A50 futures were up about 2.3%.

($1 = 7.0665 Chinese yuan renminbi)