A three-day sell-off has taken the Australian sharemarket back to levels last seen in early May, as falling commodity prices and upcoming events such as a US interest rate decision and the 'Brexit' vote take their toll on investor confidence.

The local bourse closed near the session's lows on Thursday with the benchmark S&P/ASX200 index dropping 0.8 per cent to 5278.9 - its lowest close since May 4 - and the broader All Ordinaries losing 0.7 per cent to 5324.2.