The disaster has stunned South Korea where there has been widespread public anger directed at the ferry company and crew, the rescue coordinators and the government in Seoul.
The Sewol's captain, Lee Joon-Seok, and six crew members are under arrest with two other crew taken into police custody on Tuesday.
On Wednesday morning, prosecutors raided a host of businesses affiliated with the ferry operator - the Chonghaejin Marine Company.
The raid was part of a probe into "overall corruption in management", Kim Hoe-Jong, a prosecutor on the case, told AFP.
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