BHP Billiton, the world's biggest miner, has warned that floods are continuing to affect its coal operations in Australia.
The company said in a report that output of iron ore was up 7% between January and March, compared to the same period the year before.
But output of coal fell 18% from a year earlier
BHP is the world's largest supplier of coking-coal, used to make steel, through a joint venture.
Production of metallurgical coal dropped to 6.7m tonnes between January and March from 8.2m tonnes in the same period last year.
Floods' impact
BHP's coal production is mainly in the Bowen Basin, in the northeastern part of Australia, an area that has seen record floods since the beginning of the year.
The company said wet conditions were likely to continue to affect its operations in the Bowen Basin for the rest of the year.
"Sales and unit costs are likely to be impacted, to some extent, for the remainder of the 2011 calendar year," BHP said in the report.