Stock markets in India and across the globe have tumbled. At home, the Sensex at the Bombay Stock Exchange, which plunged a hefty 467 points in opening trade, on Friday morning, later lost even more ground and had plummeted over 700 points, to slip below the 17,000 level at one stage. After making a partial recovery, the Sensex still stood a hefty 457 points, or 2.6 percent in negative territory, at 17,237 in afternoon deals a short while ago. The Nifty at the National Stock Exchange Nifty slumped 142 points, or 2.7 percent, to 5,190.The fall on the domestic bourses followed the meltdown in the global stock markets, amid worries about the US economy, and the European debt crisis.Over in the US, the key Dow Jones Industrial Average dropped 4.3 percent, overnight, to post its biggest single-day drop since December 2008. Wall Street's S&P 500 crashed about 5 per cent, and the Nasdaq also tumbled about 5 percent. Major European markets had shed about 3 percent. Joining the global rout, Asian markets nosedived, today, with the bourses in Japan, China, South Korea, Singapore, Indonesia, Hong Kong and Taiwan tumbling between 2 percent and 5.3 percent.