The benchmark Hang Seng Index was down 335.21 points to 18,772.60 in the first 20 minutes of trade, after US stocks also tumbled on the warning from ECB president Mario Draghi that there would be no big boost in rescue funding. The blue-chip Dow Jones Industrial Average tumbled 1.63 percent on Thursday to finish at 11,997.70. European Union leaders were battling Friday over treaty change at a crunch summit on the debt crisis. The talks began on a sour note with Draghi's warning that action to buy up sovereign bonds of debt-hit countries was "limited" and "temporary". At the high-stakes talks running late into the night, leaders reached a deal in principle on tougher fiscal rules for the bloc, a diplomat said, but details still remain to be worked out.