The Western Australian government has approved on Thursday the 570-km railway corridor infrastructure project that would enable Mid-West iron-ore projects gain access to the $5.9 billion proposed deepwater port at Oakajee.

Premier and State Development Minister Colin Barnett gave the approval on the proposal submitted by Oakajee Port and Rail Pty (OPR) under the project's state development agreement.

"This approval enables OPR to proceed with detailed planning and design for a railway to bring ore from deposits from the region's north and east to Oakajee," Barnett said in The Sydney Morning Herald.

The $6 billion port and rail project earlier hit a snag in August when joint-venture partner Murchison Metals admitted it could not fund its share of one of Australia's biggest infrastructure projects.

Japanese company Mitsubishi is the other joint-venture partner. Both the WA government and the federal government contributed $339 million each to build the bulk of the Oakajee port.

OPR is a 50-50 joint venture between Murchison Metals and Mitsubishi. It was responsible for developing the 45-million-ton-a-year port and rail Oakajee project.

A recently completed feasibility study for the project has increased the estimated capital cost to A$5.94 billion from the original A$4.4 billion.

The rail line will cover east from the proposed Oakajee port through Morseby Range to a junction north west of Mullewa. It heads heads north east passing the Tallering Peak project to Weld Range, and then north to Jack Hills.