The rains set off dangerous mudslides, inundated homes and destroyed bridges
The Sewol ferry was carrying 475 passengers and crew when it capsized on Wednesday. The government has said nine people were found dead and 179 had been rescued, leaving about 290 people, most of them teenaged school children, missing and possibly trapped in the vessel.
The captain, identified as Lee Joon-seok, 69, is being questioned by the coastguard and is the subject of a criminal investigation, a coastguard official said.
Media reports said he was facing the possibility of charges of negligence leading to death and also for violating a law that stipulates the conduct of shipping crew. Coastguard officials could not be reached for further details.