Five mainstream banks in South Korea plan to shut down more than 100 branches next year amid the growing popularity of on-line banking services, industries sources said Saturday.

Woori Bank, the No. 2 lender, is moving to close up to 40 of its 958 outlets across the country in 2016 as the financial company seeks to remove less profitable units.

"It could still change because we have not made a final decision, but about 30 to 40 outlets will be closed down," a bank official said.

NH Nonghyup Bank, which owns the biggest number of outlets at 1,169, is also preparing to shut down 20 next year before opening 10 new outlets in new locations.

KB Kookmin Bank, the No. 1 player, already eliminated 21 outlets last month, many of them in university districts, and plans to remove 23 more next year due to unprofitability, according to the industry sources.

How many outlets Shinhan Bank and KEB Hana Bank plan to close next year is still unknown, but sources said they will also implement some downsizing measures.

Those moves reflect the increasing popularity of mobile banking services, with the Bank of Korea's data showing that smartphone-based banking service users exceeded an accumulated 60 million as of the end of September.

The planned debut of Internet-only banks, like Kakao Bank and K-Bank will put further pressure on traditional financial lenders.

"Bank transactions are increasingly moving to mobile platforms," a Shinhan Bank official said, adding that outlets that are most affected by the mobile trend will be the first to be closed. (Yonhap)