The Sensex at the Bombay Stock Exchange declined 68 points, or 0.4 percent, to close at 18,665, amid weak Asian and European markets, today. The Nifty at the National Stock Exchange dropped 23 points, or 0.4 percent, to 5,519.Stock markets in Japan, Hong Kong, South Korea and Singapore slipped between 0.7 percent and 4 percent.