"So far, we have a total of 78 injured, all of them lightly," a spokesman for the Seoul emergency services told AFP. One TV news channel put the number of injured at 170.
News of the accident broke as the country was still reeling from a ferry disaster on April 16 that left around 300 dead or missing -- most of them schoolchildren -- after the boat capsized and sank.
The tragedy triggered widespread public anger and a bout of national soul-searching as to whether the country had sacrificed safety standards in its rush for economic development.