Indian stock market saw massive rallies at open on Thursday as Union Finance Minister Nirmala Sitharaman announced the new two-slab GST structure. Sensex jumped nearly 900 points to cross the 81,000 mark while Nifty jumped nearly 300 points to near the 25,000 mark. The rally in Nifty stocks was led by automobile and FMCG stocks, along with financial services stocks.