The most-traded iron-ore for January delivery on China's Dalian Commodity Exchange dropped as much as 6.8% to 722 yuan ($111.88) a tonne, its weakest since February 4, before ending daytime trading at 723 yuan.
Iron-ore's most-active October contract on the Singapore Exchange sank 8.3% at $131.10 a tonne by 0725 GMT.
Imported iron ore stocked at ports in China, the world's top steel producer, climbed to 131.40-million tonnes last week, the highest since end-April, SteelHome consultancy data showed.
Spot iron-ore in China tumbled to a two-week low of $145.50 a tonne on Friday, SteelHome data showed.
Iron-ore prices have fallen under the weight of "a monstrous four-million tonne" increase in weekly shipment from Australia in the last week of August, said Navigate Commodities MD Atilla Widnell.
Chinese iron-ore producers' plan to increase their domestic output by more than 100-million tonnes between 2021 and 2025 also added some pressure on prices, he said.
Some industry data showing China's weekly steel output had increased may have also prompted the continued iron ore sell-off, Widnell said.
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