That level of attrition is way too high for any job that people are voluntarily signing up for. Something is fundamentally wrong if more than half of the new joiners are leaving within a week. It must be horrendously inefficient and the existing staff trying to bring new people up to speed will get fed up and lose confidence in the process, just do the bare minimum because they think it is a waste of time, thus perpetuating the cycle.
Maybe the recruitment process isn't honest enough and people are getting the wrong expectations about what the job entails. Get people on the shop floor to refine the job specs to match reality and don't sugar-coat what you are needing people to do.