In a boost to Australia's iron ore exporters, their biggest foreign rival will export 7 per cent less than expected in the first three months of 2020, and has signalled that it will require everything to go right to achieve its full-year iron ore targets.

A weak start to the year by Brazilian miner Vale is the latest factor to roil iron ore markets, which are caught between weakening demand in China because of the coronavirus and disruptions to supply like the cyclone that blew through Western Australia last week.