US stocks extended losses on Tuesday with the S&P 500 breaking below a key support level before the start of first-quarter earnings season. The S&P 500 fell more than 1 percent in midday trade to slide below its 50-day moving average of 1,372.30, an area viewed as the support level that will make or break the current uptrend. The market's losses were broad, with the industrial and materials sectors representing the stocks suffering the biggest declines. The CBOE Volatility Index or VIX, Wall Street's fear gauge, jumped 8.3 percent to 20.39, and was up for the eighth straight day, its longest streak of consecutive gains in nearly nine years. At its session high, the VIX earlier touched 20.98 - up 11.5 percent for the day. Apple shares dropped quickly from hitting a new high of $644 per share to briefly top a $600 billion market capitalisation. At midday, the stock was down 0.3 percent at $634.51. The Dow Jones industrial average was down 168.21 points, or 1.30 percent, at 12,760.44. The Standard & Poor's 500 Index was down 19.44 points, or 1.41 percent, at 1,362.76. The Nasdaq Composite Index was down 45.80 points, or 1.50 percent, at 3,001.28.