Passenger jets are parked on the apron of Gimpo International Airport, in this undated file photo. Yonhap

Korea's low-cost carriers (LCCs) are ramping up cargo operations and cutting costs to cushion what is expected to be a sharp second-quarter earnings downturn, as prolonged high fuel prices and a weak won continue to erode their profitability.

Facing mounting losses in their core passenger businesses, airlines are seeking to offset earnings pressure by expanding freight operations while implementing cost-saving measures such as unpaid leave for cabin crew.

The deteriorating business outlook has also weighed on investor sentiment, with shares of major listed LCCs posting double-digit declines over the past three months despite the broader rally in the benchmark KOSPI.

Shares of Jeju Air dropped 14.85 percent over the past three months, and Jin Air shares saw losses of 19.03 percent during the same period.