The company said the two ship-loaders would increase the reliability of its inner harbour port facilities.

Each ship-loader will have a loading capacity of 12,500 tonnes per hour.

The existing ship-loaders, which are more than 40 years old, load iron ore at a rate of approximately 10,000tph.

The increased loading capacity will create additional loading capacity that will contribute to debottlenecking initiatives to increase the capacity of the supply chain towards 270 million tonnes per annum at a low capital cost.

“This is an important investment that is consistent with our commitment to maximise the capacity of the Western Australia iron ore inner harbour and deliver substantial value to shareholders and other stakeholders,” BHP Billiton Iron Ore president Jimmy Wilson said.

Commissioning of the two replacement ship-loaders is scheduled for the second half of 2014.

Last year, BHP commissioned the seventh and eighth ship-loaders at Nelson Point, which have a combined capacity of 35-40Mtpa.

Supply chain optimisation in the September quarter resulted in BHP lifting its WAIO guidance for the 2014 financial year to 212Mt from 207Mt.

The company said that longer term, there was the low-cost option to expand Jimblebar to 55Mtpa, with further debottlenecking of the supply chain expected to take the WAIO to 260-270Mtpa.

The Jimblebar mine near Newman was due to be formally opened today by WA Premier Colin Barnett but the ribbon-cutting ceremony was cancelled last night due to unsafe airport conditions.

Shares in BHP last traded A16c higher at $37.89.