Two first mates, one second mate and a chief engineer have been detained on allegations they failed to protect passengers, according to the Associated Press news agency.
The four crew members are also reportedly accused of abandoning the ship.
AP says prosecutors are considering whether to apply for a formal arrest warrant to allow for a longer period of investigation.
The ferry's captain and two other crew members have already been arrested on suspicion of negligence and abandoning people in need.
More top news
Detectives are exploring the movements and criminal past of the middle-aged murderer of many aliases who wrought carnage in central London.
Disney boss Bob Iger said Carrie Fisher appears "throughout" Star Wars Episode 8 Jedi and nothing would be changed using special effects.
In an embarrassing setback for the president, Republicans failed to reach the number of votes to pass his new healthcare act into law.