State radio said the MV Bukoba, carrying over 600 passengers went down at 0600 GMT. More than 40 survivors had been rescued and 21 bodies recovered. "There's no hope of recovering more survivors. We fear more than 500 people have died but rescue efforts are continuing." Sources said the elderly Bukoba was due to be taken out of service very soon. President Benjamin Mkapa has declared a three-day period of national mourning.