The Australian sharemarket extended its frantic sell-off into fourth week on Monday as unscheduled, aggressive rate cuts from the Federal Reserve and Reserve Bank of New Zealand added more fuel to the market volatility seen in the last few weeks.

The S&P/ASX 200 Index plummeted 537.3 points, or 9.7 per cent, to 5002, the local market's heaviest loss since the Black Monday crash in 1987.