Iron ore for May delivery on China's Dalian Commodity Exchange ended the morning trade 1.5% lower at 634.50 yuan ($99.68) a tonne.
The benchmark contract, however, was on course for its third straight weekly rise, supported earlier this week by optimism about China's stimulus measures to bolster its economic growth and policy support for its debt-saddled property developers.
Iron ore's most-active January contract on the Singapore Exchange slipped 0.3% to $108.85 a tonne.
"The iron ore port inventories build through recent weeks is a bearish signal and they are expected to continue to lift over the next 2-3 months as pig iron production is not likely to pick up until after the (Beijing) Winter Olympics," Westpac senior economist Justin Smirk said in a note.
Imported iron ore stocked at Chinese ports reached 155.4 million tonnes last week, the highest since July 2018, according to SteelHome consultancy data.
While falling steel inventories in China may signal an improvement in downstream demand, Smirk said current levels were still at a five-year high, suggesting "it has a long way to go before it signals a tight market".
Iron ore prices could hit $75 a tonne by end-2022, he said, as tight steel production controls to curb emissions in China are likely to remain in place.
