The Australian stock market has shrugged off an emergency rate cut from the Reserve Bank, hitting a fresh four-year low in the process, while the Australian dollar has sunk to an 18-year low.

The benchmark S&P/ASX200 finished down 170.3 points, or 3.44 per cent, to 4,782.9, while the broader All Ordinaries index sank 189.4 points, or 3.79 per cent, to 4,809.4.

The Australian dollar plunged on the RBA’s emergency measures, buying just 55.76 US cents, down from 59.98 US cents on Wednesday.