The Sensex at the Bombay Stock Exchange fell 126 points, or 0.7 per cent, to 18,459, in opening trade, today, on fresh selling by investors, amid weak Asian bourses. Later, the Sensex remained weak, and stood 140 points, or 0.8 percent in negative territory, at 18,445, in afternoon deals, a short while ago. Asian markets in Japan,China, Indonesia, Singapore, South Korea, and Hong Kong were down by between 0.3 percent and 1 percnt, on worries that China will further tighten monetary policy.