Two others were still missing as of 1:00 pm (0400 GMT), it added.
The Coast Guard had earlier said seven people were dead after a South Korean chartered fishing vessel collided with a tanker and capsized, adding two people went missing.
Local media reported the 9.77-ton chartered fishing boat, with two crew members and 20 passengers on board, collided with the 336-ton tanker in the waters near Yeongheung Island, west of Seoul, at around 6:12 am (2112 GMT Saturday) on Sunday.
South Korean authorities have mobilized four helicopters and 14 boats for the rescue operation.
