Fortescue Metals Group has borrowed $US1.5 billion ($A1.44 billion), half a billion more than initially intended, to fund the iron ore miner’s expansion plans.

Fortescue said in a statement on Wednesday that it had increased the amount of senior unsecured notes from the initial offering of $US1 billion because of strong demand.

The notes are expected to settle on October 28.

Fortescue said it intended to use the proceeds to expand its annual production rate to 155 million tonnes per annum by moving to two ports and three hubs.

The notes will have an interest rate of 8.25 per cent per annum and have an eight year term with a four-year non-call period.