HONG KONG — Hong Kong authorities are fighting an increasingly uphill battle to defend the currency peg to the U.S. dollar, intervening 49 times over a 12-month period to keep the Hong Kong dollar within the official trading band.

The Hong Kong dollar’s trading range is set between 7.75 and 7.85 against the greenback. Whenever the currency touches the lower end of the band, the Hong Kong Monetary Authority steps in to buy the local currency, driving up the cost for the de facto central bank.