The explosion occurred on Lake Suviana, in the Apennines near Bologna, and has resulted in three confirmed deaths.
Five people were also seriously injured.
“We are not working with much hope of finding the missing people alive,” said Fire Brigade Communications Director Luca Cari.
“The scenario we have in front of us does not give us the idea this is likely.”
The confirmed victims of the disaster were 36, 45 and 73 years old.
The victims, the missing and the injured were technicians from external contractors working at the plant.
The search for the missing is hampered by the fact there is lots of rubble and many areas are flooded after a turbine exploded.
The CGIL trade union said Wednesday that it had not yet been possible to ascertain who the victims of the explosion were employed by.
Bologna CGIL Secretary Michele Bulgarelli said that two of the three people who were seriously injured were Enel employees.
“What is serious is that we do not know which companies the external workers were employed by,” Bulgarelli said after arriving at the plant.
“We found out that one [of the victims] is a 73-year-old pensioner with a VAT number [for the self-employed].
“What kind of world of work is this?”
ANSA