At lunchtime AEDT on Monday, the benchmark S&P/ASX200 index was down 21.8 points, or 0.26 per cent, to 8,274.2, while the broader All Ordinaries was down 28.3 points, or 0.33 per cent, to 8,522.0.
Barring an afternoon turnaround, the ASX's losing stretch will equal a similar five-day streak from April 11-17.
Capital.com analyst Kyle Rodda said there was a degree of caution in markets at the start of a busy week of central bank meetings, especially over the Fed meeting, although the futures market was assigning less than a seven per cent chance the US central bank doesn't cut rates on Wednesday.
Five of the ASX's 11 sectors were lower at midday and four were higher, with the bourse's two consumer sectors both basically flat.
Materials/mining was the biggest mover, dropping 1.2 per cent as the price of iron ore fell.
BHP and Rio Tinto were both down 1.4 per cent, while Fortescue had fallen 2.3 per cent.
Goldminers were also down as the precious metal traded around $US2,652 an ounce, with Newmont falling 3.3 per cent and Evolution down 1.6 per cent.
The big four banks were mostly higher, with ANZ and NAB both up 0.2 per cent and Westpac advancing 0.4 per cent. CBA was the outlier, basically flat at $158.15.
Insurance companies were faring better, with IAG and Suncorp both up 1.3 per cent.
The Australian dollar was up 63.71 US cents, from 63.58 US cents at Friday's ASX close.
41°C