Spot prices for coking coal are rising on world markets as a result of the Queensland floods.
State Premier Anna Bligh says three-quarters of the coal mines in the state are currently unable to operate because of the Queensland flood.
Railway lines to transport the coal to ports for export are also flooded.
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.
Ms Bligh says the disaster is unprecedented and the overall bill could be well above $A5 billion.
Anglo American says it could be some weeks before the floodwaters can be drained from its mines.
The company has five coal mines in the Bowen Basin in central Queensland, three of which are flooded and the other two cut off.
A company spokesperson told Summer Report that stranded personnel will assess the damage as soon as possible.
The BBC reports the situation in Queensland is being closely watched by the global steel industry, because it exports half the coking coal needed to make the metal.
The price of Queensland coking coal has jumped to $US253 per tonne from $US225 in the past three weeks.
Prices peaked at $US305 during the last serious flooding in the state in 2008.
Meanwhile, the global spot price of coking coal is now around $US250 per tonne, 11% higher than the most recent long-term contract deal price of $US225.
Royal Bank of Canada senior strategist Sue Trinh told the ABC that the overall impact on trade could be up to $A9 billion in lost export income, cutting about 0.5% from Australia's economic growth.
Given Queensland represents about well over 50% of Australia's coal exports, the fact that a lot of these potential coal exports have been stalled is likely to result in weaker export revenues and growth in the very near term for Australia, she said.