Propelled by a rally in the global stock markets, the Sensex at the Bombay Stock Exchange surged 287 points, or 1.7 per cent, to 17,634 in early trade, today, on heavy buying by funds and retail investors.Later, the Sensex gained even more ground, and stood a hefty 321 points, or 1.9 percent in the positive zone, at 17,667 in afternoon deals, a short while ago. All the sectoral indices were trading higher, with gains of up to 2.2 per cent.Stock across the world also rallied, after the European Central Bank announced an unlimited bond-buying program to reduce borrowing costs for the region's most indebted nations, boosting demand for riskier assets. So key stock indices in Japan, China, Hong Kong, Indonesia, South Korea, Singapore and Taiwan posted strong gains of between 1 percent and 4 percent, today.Across on Wal Street, the key Dow Jones Industrial Average had spurted 1.9 per cent in yesterday's trade.