SYDNEY (AFP) - The son of Australia's richest person Gina Rinehart, who is embroiled in a family feud, has withdrawn his bid to head a family trust for "the sake of family harmony", reports said on Wednesday.

The feud has been simmering since 2011, with son John Hancock siding with his sister Bianca Rinehart against their mother for control of the multi-billion dollar trust.

At the centre of the dispute is the trust set up by the late mining magnate Lang Hancock in 1988 with his four grandchildren as the beneficiaries.

His daughter Ms Gina Rinehart was to run the trust, which holds a 23.4 per cent share of her iron ore company Hancock Prospecting, until the youngest grandchild turned 25 in 2011.

But just days before this date Ms Gina Rinehart allegedly sought to delay the payout until 2068, saying it would avoid a huge capital gains tax bill.

The move prompted Mr Hancock and sisters Ms Bianca Rinehart and Ms Hope Rinehart Welker to take court action, although Ms Hope Rinehart Welker later withdrew from the case.

Earlier this month Ms Gina Rinehart said she planned to relinquish control of the trust, and her son had appeared keen to replace her.

But Sydney's Supreme Court heard on Wednesday that Mr John Hancock had withdrawn his application to become head of the family trust in favour of his sister Bianca, the Sydney Morning Herald reported.

"I made the decision last night to ask Bianca to nominate as replacement trustee," he said in a statement. "I also decided to stand down as replacement, in the interests of family harmony, and support Bianca's nomination."

Lawyers for the youngest sister Ginia Rinehart reportedly objected to the proposal, saying if Bianca was to be trustee, it should have been mentioned months ago.