From UBS:
China’s inventories of iron ore at ports have hit all-time record highs recently of approx. 130Mt. This is a record high both in levels and in days of supply terms. Yet the market currently appears comfortable with this.
Low grade inventory has risen solidly over the last 12 months. While precise numbers are hard to verify, we understand that lower grade inventory (50%-60% Fe) has risen from ~35% of total port stocks at the start of 2016 to ~45% of total port stocks now.