Iron ore is getting beaten down after a flurry of warnings that gains may be vulnerable. Futures in China have posted an unprecedented weekly loss; the most-active contract in Singapore is lower for a sixth day; and spot prices had the biggest slump since November.

"It's an overdue correction in prices, which have risen too much," Ralph Leszczynski, head of research at shipbroker Banchero Costa & Co, said in an email on Friday, while cautioning that the drop has come despite a positive underlying picture. "Fundamentals for iron ore remain very strong at present."

Iron ore rallied last year on stronger-than-expected demand and extended gains into 2017, benefiting miners from Brazil's Vale to BHP Billiton and Rio Tinto Group, as China bought record volumes. This year's advance has unfolded against a backdrop of warnings that gains may prove fleeting, with mines continuing to expand and concerns that China's steel demand may falter. Still, imports by the top buyer are expected to be at an all-time high this month, close to 100 million tonnes, and remain strong in April, said Leszczynski.

"I don't think this is the big sell-off yet," Tomas Gutierrez, an analyst at Kallanish Commodities, said by phone from Shanghai. This week's poor performance is attributable to concerns over fresh property curbs in China, as well as uncertainty about the policy outlook from Donald Trump's administration and higher US interest rates, according to Gutierrez.

In Dalian, most-active futures collapsed 19 per cent this week - the most on record - as steel prices backtracked, with reinforcement bar in Shanghai tumbling 12 per cent. On Friday, the iron ore contract for September lost as much as 2.2 per cent to 567.5 yuan a tonne, the lowest since January 10, before ending level at 580.5 yuan.

Benchmark spot ore with 62 per cent content in Qingdao fell 1.5 per cent to $US85.06 a tonne on Friday, taking the week's retreat to 7.9 per cent, according to Metal Bulletin. In Singapore, SGX AsiaClear futures had the fourth weekly loss in five, about 9 per cent lower.

Plenty of banks and even some producers have flagged risks. Barclays said this week prices will slump into the $US50s in the second half as mills' profitability is set to drop, encouraging producers to shift consumption toward abundant lower-grade ores. The bank was restating a bearish position.

The drop has hurt mining shares. Rio declined 4.5 per cent in Sydney trading this week, wiping out most of this year's gain. In Brazil on Thursday, Vale retreated 1 per cent and is on course for a month decline.