The Sewol's captain, Lee Joon-Seok, and 10 crew members had already been arrested on charges ranging from criminal negligence to abandoning passengers.
The remaining four were arrested today after warrants were issued, prosecutors said.
The confirmed death toll from the tragedy stood today at 187, with 115 unaccounted for -- many bodies are believed trapped in the ferry that capsized on April 16 on a routine voyage to the southern resort island of Jeju with 476 people on board.
Prosecutors have raided a host of businesses affiliated with the ferry operator, the Chonghaejin Marine Company, as part of an overall probe into corrupt management.
The widening investigation has also seen travel bans put on eight current and former executives of the Korea Register of Shipping -- the body responsible for issuing marine safety certificates.
A looming storm and high tides put a temporary halt to operations to recover the remains of those still missing over a week after the disaster.
"Divers could not go deep into the ship due to strong currents today," a rescue team official told AFP.
Making up the bulk of the passengers on the 6,825 tonne Sewol when it sank were 325 high school students -- around 250 of whom are either confirmed or presumed dead.
Although all hope of finding survivors has been extinguished, there is still anger and deep frustration among relatives of the missing over the pace of the recovery operation.
Frogmen have battled strong currents, poor visibility and blockages caused by floating furniture as they have tried to get inside the upturned vessel, which rests on a silty seabed.
Even so, they are coming across horrifying scenes in the murky water, including one dormitory room packed with the bodies of 48 students wearing lifejackets.
