Giving up all its initial gains, the Sensex at the Bombay Stock Exchange declined 252 points, or 1.2 percent, to close below the 21,000-level, at 20,888 after volatile trade, on late profit-booking by investors, today. The Nifty at the National Stock Exchange fell 81 points, or 1.3 percent, to 6,221.Stock markets in China, Hong Kong, South Korea and Singapore ended mixed.