Jumlah sebenar penumpang belum disahkan.
Dua orang dilaporkan maut dan lebih 100 belum ditemui.
Setakat ini 368 orang telah diselamatkan.
A major rescue operation is under way, involving 34 naval, coastguard and civilian ships, and 18 helicopters.
The ferry, carrying mainly school students, was travelling from the port of Incheon, in the north-west, to the southern resort island of Jeju.
Images showed the ferry listing at a severe angle and then later largely submerged, with only a small part of its hull visible.
Sumber: BBC News