SYDNEY, Jan 21 (Reuters) - BHP Billiton said on Wednesday iron ore output climbed 16 percent to 56.35 million tonnes in the December quarter, fuelling concerns big mining houses would continue to saturate an already over-supplied global market
The world's third biggest iron ore miner also said it would boost annual output by 11 percent in fiscal 2015 to a total 225 million tonnes.
The sharp quarterly increase over the year-ago period comes a day after Rio Tinto unveiled a 12 percent rise in quarterly output. Iron ore prices .IO62-CNI=SI have dropped to around $68 a tonne from $135 a year ago.
Analysts estimate oversupply had reached as much as 60 million tonnes by the end of 2014, with mines in China also running hard, despite a cost disadvantage to foreign producers. (Reporting by James Regan; Editing by Richard Pullin)