Chinese-linked companies have applied to the Foreign Investment Review Board over a big investment involving Fortescue Metals Group.

Details are pretty thin, but media reports say it is not a move to take over Fortescue.

Instead, the companies appear to be looking at buying a stake in FMG, or possibly buying some of its rail and port infrastructure.

China's largest steel producer, Baosteel, and China's largest conglomerate, CITIC, are strongly rumoured to be part of the deal, as both have been in discussion with FMG about a recapitalisation.

Fairfax Media reports say the deal could involve a partial selldown of stock by the company's founder, chairman and biggest shareholder, Twiggy Forrest.

Fortescue built its business using big loans from local and international providers. But its debt-based progress has put FMG under pressure several times in the face of weak ore prices.

Mr Forrest has previously talked about possibly selling a stake in the company's mining assets, and even offloading part of his own 30 per cent equity holding.

The FIRB applications by unnamed groups were reported by veteran journalist Laurie Oakes on the weekend.

FMG faces a massive $US4.9 billion debt repayment in 2019, and with its assets – mainly its mine and rail assets – valued at around $US18 billion, there is strong speculation that these will be part of the move to shore up the balance sheet.

More details, and possibly an official announcement from the FIRB, are expected soon.