Mumbai, Oct 4 Caution ahead of a likely hike in key lending rates by the Reserve Bank of India (RBI), along with a weak rupee and high crude oil prices, pulled the Indian equity indices deep into the red on Thursday.Additionally, the outflow of foreign funds, combined with heavy selling pressure in oil and gas, auto and healthcare counters subdued investors' sentiments.The S&P BSE Sensex plunged by over 800 points, while the NSE Nifty50 lost over 300 points.Index-wise, the wider Nifty50 of the National Stock Exchange closed at 10,599.25 points, lower 259 points or 2.39 per cent from its previous close.The S&P BSE Sensex, which opened at 35,820.53 points, closed at 35,169.16 points, down 806.47 points or 2.24 per cent, from its previous close of 35,975.63 points.It touched an intra-day high of 35,820.53 points and a low of 35,022.12 points.The barometer Sensex has lost over 1,300 points during the last two sessions, while the NSE Nifty50 lost over 400 points."It was the second consecutive session of losses for the Nifty. Bluechip stocks came under heavy selling pressure on the back of a falling rupee and surging crude prices," Deepak Jasani, Head of Retail Research at HDFC Securities, said."Negative global cues also impacted market sentiments."Currently, Brent crude oil price hovered around $86 per barrel.On the currency front, the Indian rupee closed at 73.58 per US dollar, 24 paise weaker from its previous close of 73.34. It crashed to a low of 73.77 (73.7688) earlier in the day.According to Vinod Nair, Head of Research, Geojit Financial Services: "Selling intensified across sectors as apprehensions over currency and yield turned to reality due to deteriorating macros.""Even after the fall in the market, valuations remain expensive at 17x with the mid-cap at 18x. Market acted proactively ahead of RBI policy in expectation of 25 basis points rate hike while any steps to contain the liquidity crunch will give support to the market."The RBI's fourth bi-monthly Monetary Policy Committee (MPC) meet during the current fiscal ends on Friday, October 5. The apex bank is widely expected to turn more hawkish in its monetary policy stance due to a rise in inflationary pressure.Investment-wise, provisional data with the exchanges showed that foreign institutional investors sold stocks worth Rs 2,760.63 crore and domestic institutional investors bought stocks worth Rs 1,823.59 crore.The top Sensex gainers were: ICICI Bank, up 4.07 per cent at Rs 315.95; Axis Bank, up 2.70 per cent at Rs 586.10; Larsen and Tubro, up 1.18 per cent at Rs 1,259.15; Yes Bank, up 1.08 per cent at Rs 215.15; and Mahindra and Mahindra, up 0.52 per cent at Rs 795.25 per share.On the other hand, major losers included Reliance Industries, down 7.03 per cent at Rs 1,120.55; Hero Moto Corp, down 5.45 per cent at Rs 2,757.00; Tata Consultancy Services, down 4.54 per cent at Rs 2,064.25; Adani Ports, down 4.17 per cent at Rs 315.95; and ONGC, down 3.74 per cent at Rs 174.80 per share.