Mumbai- Sensex at BSE lost considerably more ground, and had plunged 434 points, or 1.4 percent, to 31,489, a short while ago.The Nifty at the National Stock Exchange had slumped 138 points, to 9,826. Selling pressure was seen across the board.Key regional stock markets in China, Hong Kong, Singapore and South Korea had fallen between 0.1 percent and 1.4 percent, amid geopolitical worries, and concerns about the Chinese economy.Rupee had weakened 16 paise, to 64.95 against the dollar in afternoon deals.