Gina Rinehart's family feud has stepped up a notch, with youngest daughter Ginia releasing private emails sent by her brother John to their mother in which he described Ginia as "incompetent, craving attention and superficial" with a brain like ''a weak bowl of porridge''.

John Hancock, 38, sent one of the emails in February last year, just days after a suppression order was lifted and the family's mammoth dispute was aired.

More dirty laundry for Gina Rinehart, left, as emails are revealed. Credit:Andrew Meares

He told his mother that Ginia, then 25, could not help run the company because "you have spoiled her so much her brain has turned into a weak bowl of porridge'', according to an affidavit tendered by her lawyer, John Dalzell.

The bitter dispute erupted days before Ginia was to turn 25 the previous September, a trigger for vesting of a $5 billion trust set up by their grandfather Lang Hancock.