Trading of iron ore derivatives on China's Dalian Commodity Exchange climbed to a record last month as prices increased.

Volume jumped 33 per cent in May from a month earlier to 24.86 million contracts, or 2.49 billion metric tons, according to bourse data. The previous all-time high was set in April. Compared with a year earlier the volume more than tripled.

Iron ore prices advanced in May as port stockpiles in China contracted. The world's biggest consumer of metals and energy is seeking to expand its role in setting benchmark raw-material prices. A priority for the Dalian bourse this year is boosting the influence of its prices on global trade, according to Chen Wei, head of industrial commodities.

"Sentiment toward iron ore improved recently and there's speculation prices have bottomed," Li Jinlu, an analyst at Yongan Futures in Shanghai, said by phone. "While some are still bearish on China's economy and its demand, the divergence between these views caused greater volatility."

Open interest, or the number of outstanding contracts that haven't been settled, was equivalent to 61.77 million tons in May. While that's 4.6 per cent higher than in April, it's 31 per cent below a peak in October, according to bourse data.

Trading in contracts on the Singapore Exchange totalled 71.8 million tons in May, down 8.2 per cent from April and 43 per cent higher than a year earlier, according to bourse data on Tuesday. Open interest averaged 138.1 million tons last month, more than double Dalian.

Dalian started trading iron ore futures in 2013, challenging cash-settled contracts offered by Singapore Exchange, CME Group and Intercontinental Exchange. While trade is restricted to local citizens and companies registered in China, the exchange plans to allow foreign access.

Prices of the most-active futures rose 4.5 per cent in Dalian in May to cap the first back-to-back monthly advance since trading began. Ore with 62 per cent content in Qingdao climbed 10 per cent in May, and was at $US63.02 a dry ton on Tuesday, according to Metal Bulletin Ltd.