Rescuers are working around the clock to remove passengers from the capsized ferry. South Korean KBS says although the landforms under the sea will not hamper the rescue operation, the biggest challenge rescuers face is the rapid stream.

Senior researcher of Korea Institute of Ocean Science & Technology said, "The speed of water flow is 2 meters per second. And the pressure divers feel under water amounts to over three hundred kilograms. The condition is life-threatening."

The sea are where the South Korean ferry sank is in deep of 37 meters, and the flowing speed is between 1.2 to 2.4 meters every second, which is very hard for divers to move and change direction under the sea. A reporter from KBS has experienced the risks. When the flowing speed is over 2 meters per second, a 170cm-high male could even keep himself stick to the ground.