BHP Billiton 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 through a joint venture.
Production of metallurgical coal dropped to 6.7Mt between January and March from 8.2Mt in the same period last year.
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.
BHP Billiton's production of iron ore, it biggest single commodity, jumped to 33.2Mt in the March quarter, up 7% from a year earlier, but eased 1% on the previous quarter because of Australia's wet summer.
BHP Billiton is the world's largest supplier of traded hard coking coal, via a joint venture with Japan's Mitsubishi Corp , and is also the third largest iron ore producer - positions that have enabled it to reap record profits from surging demand from Asian steel-makers.