Asked at a conference when that shift might happen, Gary Billingsley, executive chairman of the Canadian developer of rare earth mines, replied: "Perhaps beyond 2015."

Prices of rare earths, used in products ranging from handheld electronic devices to wind turbines, have soared over the past year since China sharply cut its export quotas on them, leaving Western companies scrambling to redevelop mines idled decades ago.

The head of US producer Molycorp Inc last week made a similar prediction for when China could become a net importer of the materials.