Mumbai, April 21 : The key Indian equity indices plunged over 2 per cent on Tuesday tracking weakness in global markets. The slump in the stock markets globally came on the back of the huge crash in the US crude oil prices. In a historic price movement, the futures of WTI crude in the US for the first time fell below zero and turned negative. However, the May contract of WTI crude on the NYMEX has turned positive and is currently trading at $1.38 per barrel. Following the crash, all Asian stock markets traded in the red. At 10.13 a.m., Sensex was trading at 30,777.36, lower by 870.64 or 2.75 per cent from the previous close of 31,648.00. It had opened at 30,836.19 and has so far touched an intra-day high of 30,900.12 and a low of 30,634.41. The Nifty50 on the National Stock Exchange was trading at 9,005.25, lower by 256.60 points or 2.77 per cent from the previous close. /IANS