Building on initial gains, the Sensex at the Bombay Stock Exchange had surged 283 points, or 1.5 percent, to 19,800 in afternoon trade, a short while ago. Earlier in the morning, the Sensex had climbed 156 points, or 0.8 percent, to 19,674, on continued buying by funds and retail investors.Stock markets in Japan, Hong Kong, Singapore, Taiwan and Indonesia were trading mixed, today. But over on Wall Street, the Dow Jones Industrial Average had lost 0.4 percent, yesterday.