The vessels, commonly labelled "car ferries" in South Korea as they mainly carried passengers and cars pre-Covid, have been filled by cargo as tourism ground to a halt in the pandemic, reports UK's The Loadstar.

Exports accounted for 225,600 TEU of 2021 volumes, while imports comprised 445,500 TEU. Ro-ro ferry services commenced between China and South Korea in 1990, when the countries established diplomatic relations in the last days of the cold war.

Container volumes going by ferry last year rose 20 per cent on 2020, when 559,400 TEU was transported - just 2 per cent up on 2019 - indicating that more shippers turned to ferries as logistical bottlenecks intensified in 2021.

But, as liner operators upped freight rates, the Ministry of Oceans and Fisheries said ro-ro ferry operators had kept their rates unchanged in 2021, at around US$300-$350/TEU. However, the surge in bunker prices amid the Russia-Ukraine war is expected to mean higher freight rates this year.

With the exception of September, every month last year saw double-digit growth in earnings. Particularly, in January and February, when they soared by 45 per cent and 35 per cent year on year, respectively, due to the low base in the pandemic's early days.

And among the 12 South Korea-China ferry operators, Rizhao International Ferry carried the most containers last year, 67,600 TEU between Pyeongtaek in South Korea and Rizhao in China. This was up 30 per cent on 2020. In second place was Huadong Shipping, which carried 65,700 TEU between Incheon in South Korea and Shidao in China, up 20 per cent year on year.