Investors remain unsure as to when it will be safe to catch the falling knife that is iron ore prices, with the commodity again sinking to a new five-year low overnight.

At the end of the offshore session on Wednesday, benchmark iron ore for immediate delivery to the port of Tianjin in China was trading at $US70 a tonne, down 3 per cent from its previous close of $US72.10 and off over 7 per cent across the past two trading days.

This week’s sharp falls have stirred a heavy sell-off in the stock of iron ore miners, with Fortescue Metals Group, BC Iron and Mt Gibson among the hardest hit, with double-digit percentage declines. All three are now trading at 52-week lows and have lost more than 50 per cent of their value since the start of the year.

Diversified giants BHP Billiton and Rio Tinto have held up comparatively well, but are still losing ground in otherwise flat markets. Both firms saw their UK-listed stock give up 2 per cent in overnight trade, representing their worst offshore session for the week and pointing to another day of red numbers on the ASX.

The commodity has now lost close to 50 per cent of its value this year as investors head for the exits during a period of rapid supply increase from mining heavyweights and demand weakness from key consumer China.

After a strong October, the commodity is now on track to record its fourth straight double-digit quarterly percentage decline.

The latest moves come after BC Iron yesterday hinted at confidence in a near-term recovery as the firm sees the price of the commodity fall below its rumoured breakeven level.

“We believe the iron ore price will improve as China and other customers in different markets continue with infrastructure development and general economic growth,” BC Iron chairman Anthony Kiernan said.

Such confidence has not been shared by analysts of late, with banks continuing to revise their forecasts lower.

Last week, both ANZ and Citi analysts slashed their forecasts for iron ore in the coming years, with ANZ confident that the $US100 a tonne mark will not be seen in the medium-term.

ANZ tipped a floor at around the $US70 a tonne level, but based on last night’s moves, Citi’s prediction of the commodity sinking below $US60 a tonne at some stage in the next 12 months appears well within reach.

Commonwealth Bank’s commodity desk is also rewriting its expectations, warning that predictions for a restocking in China to round out the year may come to naught, placing further pressure on prices.

"We no longer expect a meaningful iron ore restock later in the year as steel mills in China are content to purchase iron ore at their convenience," the bank said.

"The fall in prices is consistent with expectations amongst Chinese steel mills who are anticipating iron ore to fall under $US70 a tonne in the 2015 first half."

BHP today holds its annual general meeting in Adelaide, with plenty of questions tipped to fly about its strategy to raise supply during a period of plummeting prices.