HK, China shares in weak finish to big 2nd quarter

* HK shares mark best quarter in 15 years

* China shares tack on 63 percent in first half

* Sinopec gains after China's surprise fuel price increase (Updates to close)

By Parvathy Ullatil and Claire Zhang

HONG KONG/SHANGHAI, June 30 (Reuters) - Hong Kong shares finished their best quarter in more than 15 years with a whimper on Tuesday, as investors locked in some of the gains made during a stellar four-month rally that began in March.

The index tacked on 35.4 percent in its biggest quarterly advance since the Oct.-Dec. period in 1993 when low interest rates in the U.S. and China's economic awakening drove investors into Asia's high-growth "tiger" economies.

Chinese stocks snapped a four-day winning streak on Tuesday, as steel and auto shares fell, but they added a quarter to their value in the second quarter fuelled by signs of economic recovery and ample liquidity in the financial markets.

But the strong rebound in share valuations, which has outstripped the recovery in real economic activity, has made analysts cautious about the market's prospects in the second half.

"Investors wouldn't dare be too optimistic about first-half earnings, while the pace of IPOs will also be in focus in the third quarter," said Western Securities analyst Cao Xuefeng.