Rio Tinto has requested a trading halt on its shares as it seeks subscribers for a shortfall in its Australian rights issue.

Rio said on Friday it had attracted 94.76 per cent take up of the new shares it offered as part of a 21 for 40 rights issue, totalling 142,149,887 shares.

The Australian leg of the issue raised $A4.02 billion.

As part of their underwriting obligations, JP Morgan and Macquarie are seeking subscribers for the remaining 7,865,410 new shares offered through the Australian-listed Rio entity, by way of a bookbuild to be undertaken on Friday.

"Rio Tinto Limited will be requesting a trading halt to facilitate this process," the miner said.

Earlier on Friday, Rio said says it had sold the last the remaining shares offered in its rights issue in the United Kingdom, with two brokers finding buyers after the issue had closed.

Credit Suisse and JP Morgan Cazenove found buyers for 15,882,790 new Rio Tinto plc shares offered at 2,100 pence.

When the issue closed, Rio had placed 96.97 per cent of new shares offered.

Rio's major shareholder, Chinese government-owned Chinalco, has said it would take part fully in the rights issue.

Chinalco's shares in Rio are through the UK-listed entity.