The Indian equity benchmarks extended gains after staging a gap up opening on the last day of calendar year of 2021 powered by gains in index heavyweights like Reliance Industries, ICICI Bank, HDFC Bank, Axis Bank, HDFC and Kotak Mahindra Bank amid mixed trend in global markets. The Sensex rose as much as 510 points and Nifty 50 index touched an intraday high of 17,359.