September iron ore on the Dalian Commodity Exchange ended daytime trading 5.7% lower at 1,142.50 yuan ($177.40) a tonne, after earlier hitting a three-week low of 1,102 yuan.
Extending overnight losses, Dalian's most-active contract has fallen 16% from a record 1,358 yuan hit on May 12.
On the Singapore Exchange, the most-traded June iron ore fell 3% to $200 a tonne by 0706 GMT. It touched a record peak of $233.75 on May 12.
China, the world's biggest producer of steel products, has sharply increased consumption of iron ore and other steel ingredients while ramping up output for use in producing home appliances and construction materials, amid robust demand spurred by global stimulus measures.
That propelled prices to record peaks this month, with spot iron ore soaring beyond $200 a tonne.
