The S&P BSE Sensex and NSE Nifty 50 indexes witnessed sharp declines today after the government data on Friday showed that the country's economic growth fell to over six-year low of 5 per cent against an estimate of 5.7 per cent compiled by a Reuters poll. Weakening economic growth along with escalating US-China trade frictions are hurting the market sentiment, analysts said. The Sensex and Nifty posted their biggest single-day fall since July 8. The Sensex slumped 770 points or 2 per cent to settle at 36,563 and the NSE Nifty 50 index dropped 225 points or 2 per cent to close at 10,798.