South Korea might need as many as 15 million immigrants—equivalent to a third of its current population--by 2060 to make up for a shrinking workforce and sustain growth, according to a Seoul-based private think tank.

The report, released Monday by the Korea Economic Research Institute, describes a demographic profile quite different from present-day South Korea, which is a highly homogeneous society where immigrants constitute just 3% of the nation's 50 million people.

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