Iron ore futures in China slipped on Wednesday, retreating after two straight session of gains in low volumes as many overseas markets were closed for the Christmas holiday.

The most actively traded iron ore futures on the Dalian Commodity Exchange, for May 2020 delivery, closed down 0.2% at 639 yuan ($91.48) per tonne, giving up gains from early trade.

The total trading volume of iron ore futures contracts was 1.17 million lots, compared with 1.92 million lots on Tuesday.

Prices were also subdued as heavy-pollution alerts in China's northern province disrupted demand for the steelmaking raw material.

The air quality index in top steelmaking cities Tangshan and Handan exceeded 150 on Wednesday, indicating medium to heavy pollution, data from the Ecology and Environment Ministry showed.

Prices for spot cargoes of iron ore with 62% iron content for delivery to China fell $1 to $92.5 per tonne on Tuesday.

Other steelmaking ingredients were mixed, with Dalian coking coal dipping 0.3% to 1,152 yuan per tonne and Dalian coke inching up 0.05% to 1,846 yuan per tonne. Steel rebar on the Shanghai Futures Exchange, for May 2020 delivery, dropped 1.1% to 3,485 yuan per tonne.

Hot-rolled coil, used in cars and home appliances, fell 0.8% to 3,521 yuan per tonne.

Shanghai stainless steel futures, for February 2020 delivery, was down 0.6% at 14,240 yuan per tonne. Shanghai Futures Exchange has said it will relax trading position limits on its product contracts from next year for 37 futures trading companies to encourage trading activity and increase market participation.