The Sensex at the Bombay Stock Exchange declined 51 points, or 0.3 per cent, to 19,356, in opening trade, this morning, as funds and retail investors booked profits after a recent strong rally, amid a mixed trend in the other Asian bourses. Later, the Sensex remained weak, and stood 63 points, or 0.3 percent in the red, at 19,343 in afternoon trade, a short while ago. The Sensex had gained over 675 points in the previous four trading sessions.Stock markets in Hong Kong, Indonesia, Singapore, China, Japan and South Korea were trading mixed.