China’s iron ore imports from Australia rose 22.2 percent to 144.4 million tonnes in the first quarter from a year earlier, customs data showed on Wednesday, as major producers ramped up production and increase shipments.

Top miners Rio Tinto and BHP Billiton have boosted output, focusing on slashing costs to make returns and carve out market share as falling prices squeeze higher-cost miners.

The soaring shipments to China at a time when the country’s steel demand is slowing has meant iron ore prices have more than halved to around $50 a tonne in the past 12 months.

Amid this slump BHP Billiton said it will slow down its expansion plans by delaying an Australian port project that would have boosted output by 20 million tonnes, but Rio Tinto still plans to ship 350 million tonnes of ore in 2015.

Imports from Australia jumped 26.6 percent to 51.55 million tonnes in March from a year ago, data from the General Administration of Customs showed.

Total imports by China rose 2.4 percent to 227.1 million tonnes in the first quarter from the same period of last year.

China’s imports of iron ore from Brazil, its second-largest supplier after Australia, inched up 0.6 percent to 41.8 million tonnes in the first quarter from a year ago. Shipments in March dropped 2.5 percent to 14.48 million tonnes.