Erasing all its early gains, the Sensex at the Bombay Stock Exchange plunged 308 points, or 1.6 percent, to 18,564, in afternoon trade, a short while ago, after the Reserve Bank hiked its key policy rates by a steeper-than-expected 50 basis points. Earlier in the morning, however, the Sensex had gained 73 points, to 18,945, amid firm Asian bourses. But other markets in Japan, China, Hong Kong, Indonesia, Singapore, South Korea and Taiwan were up by between 0.1 percent and 1.2 percent, today, on hopes that US lawmakers will reach an agreement on rasing the government's debt ceiling by the August 2 deadline.