The Sensex at the Bombay Stock Exchange rose 173 points, or 0.9 per cent, to 18,936 in opening trade Monday morning, on renewed buying by investors, amid firm Asian bourses. Later, after climbing as much as 180 points at one stage, the Sensex surrendered most of its early gains, and stood a modest 48 points, or 0.3 percent in positive territory, at 18,811 in afternoon trade, a short while ago. Other Asian markets in Japan, Hong Kong, Indonesia, Singapore, South Korea and Taiwan were up by between 0.4 percent and 1.8 percent, on Monday, after US manufacturing activity unexpectedly accelerated in June.