A top coast guard official, Marco Brusco, said on state TV that 25 passengers and four crew members are unaccounted for three days after the ship crashed into a reef off the Tuscan coast and capsized.
Earlier in the day that number stood at 16.
Brusco didn't immediately explain the rise.
But at least three Italian families have said that even though their loved ones have been listed among those safely evacuated, they hadn't heard any word from their relatives.
Brusco indicated about 10 Germans were among the 29 missing. He says he holds a "glimmer of hope" that some of the missing might have survived.