Hong Kong's Hang Seng index prolonged its losses on Thursday as drop in commodity prices pressed the index into negative territory. Hang Seng index plunged 1.32% or 276.03 points and closed at 20,609.39 with energy sector posting the biggest daily drop. Aluminum Corp. of China lost 1.3% while PetroChina gave up 2%. Cnooc tumbled 3.3% despite reporting better than expected annual net income as oil provider admitted it set a conservative output target for 2012.