Currently, the port's two wharves can load 44.5 million tonnes a year. The $115 million stage six development will boost this to 55 million tonnes by the middle of 2003.
The expansion involves the construction of another wharf and the installation of a massive 1030t, 50m tall coal loader.
The extra capacity is needed to cope with an expected increase in the output of the nine existing mines, plus an extra two mines - from Macarthur Coal and MIM - due to open in the next two years.
Last year, about 42.5Mt of coal went through the port and the company claims that, in the 12 months after the new capacity comes on stream, this will increase to 51Mt.
Prime Infrastrucure, bought the coal terminal from the Queensland government for $630 million in August 2001. The company listed on the ASX earlier this year and is backed by investment bank Babcock & Brown.
The company is currently in negotiations with nine users about an access agreement that could affect the prices it gets. The submission date for the agreement, which needs to be endorsed by the state government was extended until March 14 2003.