The Indian equity benchmarks extended losses after staging a gap down opening on Wednesday mirroring losses in global markets as worries of aggressive monetary tightening amid surging inflation rattled investors' sentiment globally. The Sensex fell as much as 666 points and Nifty 50 index broke below its important psychological level of 17,800. HDFC Bank, HDFC, Reliance Industries, Infosys and Tata Consultancy Services were among the top drags on the Sensex.