The Sensex at the Bombay stock Exchange zoomed 406 points, or 2.3 per cent, to 18,428 in early trade, today, on hectic buying by funds and retail investors. Later, the Sensex remained firm, and stood 418 points, or 2.3 percent in the green, at 18,439 in afternoon deals, a short while ago. All the sectoral indices were trading higher, with gains of up to 3.4 per cent. Sentiment was boosted after the government's action on diesel prices designed to bring down its burgeoning fiscal deficit, and curb under-recoveries of public sector oil marketing companies. The markets also rose after the US central bank unveiled a fresh stimulus plan to help spur the US economy. The 30-share Sensex had gained nearly 710 points in the previous seven trading sessions.Key stock markets in Japan, China, South Korea, Singapore, Taiwan, Hong Kong and Indonesia posted good gains of between 0.5 percent and 2.8 percent, today, after the announcement of the U.S. central bank's new stimulus plan.The US Dow Jones Industrial Average had surged 1.6 per cent in yesterday's trade.