People travelling on the Discovery Bay ferry to and from Central will pay up to 21 percent more per trip from August 11.

Adult residents using Octopus Cards registered with the ferry operator will see the fare for the 25-minute journey go up from HK$33.5 to HK$38.2.

Fares will increase to HK$24 for those aged 65 or above, and to HK$19.1 for full-time students under 26, as well as children under 12.

Prices for those without registered cards will go up from HK$46 to HK$55.8, with the discounted rate for seniors and children rising from HK$23 to HK$27.9.

The increase approved by the government is lower than the 60 percent the ferry operator, Discovery Bay Transportation Services, had requested.

In a document submitted to Islands District Council, the Transport Department noted that the fares were last raised in June 2018. It said the number of passengers had dropped, while operating costs continued to rise.

"The revenue generated by the ferry service has been insufficient to cover the rising operating costs. In addition, the cumulative inflation rate has reached double digits since the last fare adjustment," the department said.

In granting the fare hike, the authorities said they had taken in account a number of factors, such as operating costs, revenues and the level of public acceptance of the increase.

The department also said the ferry operator should continue to "explore feasible measures" to improve its financial situation.