The Queensland floods have had a substantial impact on the state's coal production and wheat and sugar crops.
State premier Anna Bligh says 75% of the operations at coalfields have been halted.
The BBC reports Queensland supplies half of the world's coking coal needed in steel manufacturing.
Open-cast mines are flooded and railway lines are washed out.
Coal is Australia's top export earner, accounting for $A55 billion of export revenue each year.
Anglo American and Rio Tinto have cancelled shipments and declared force majeure.
The port of Dalrymple is open again, but nearly 50 ships are still unable to dock. At least 18 more are waiting outside the port of Gladstone, which is operating at greatly reduced capacity.
Huge effect on agricultural production
The state is also responsible for almost all the country's sugar production, but with the canefields drenched, the BBC reports, Australia will be forced to import raw sugar this year.
Canegrowers estimate that up to 18% of the 2010 harvest has been abandoned and early plantings for the 2011 crop are under water.
Australia is also the world's fourth largest wheat exporter, but almost half the crop - 10 million tonnes - has had to be downgraded.
GrainCorp Ltd said on Monday that the transportation of all grain in Queensland was at a standstill.
