The multibillion-dollar plans of BHP Billiton and Rio Tinto to secure opportunities in Guinea's resource industry have been temporarily halted because of growing security fears in the West African nation.

BHP has flown out the 20 staff it has working on it taking a lead role in a $US2.3 billion ($A3 billion) bauxite/alumina project. Rio has flown out about 60 staff involved in its Simandou iron ore project, potentially the host of a $US2 billion development.

BHP is due to commit this week to becoming the operator and lead partner in the bauxite/alumina project being promoted by Canada's Global Alumina Corp. Like Rio, BHP has become increasingly adventurous in where it is prepared to invest to secure growth.

Guinea's President Lansana Conte's declaration of martial law to quash violent protests against his 23-year rule has put the projects on hold.

BHP said yesterday it had confidence in the long-term opportunities in Guinea but the safety of its people was paramount.

Responding to reports of more than 80 deaths in the Government crackdown, the United Nations High Commissioner for Human Rights, Louise Arbour, said Guinea's security forces "must abide by international standards on the use of force". She said there had been "serious allegations of gross breaches of those standards".

Operators in Guinea's bauxite/alumina industries, including Alcoa and Alcan, have reduced operations pending an improvement in security.

Despite the dramas in Guinea — it holds a third of the world's bauxite resources — global equity markets continue to be more interested in speculation that BHP and Rio have separate plans to make a $US40 billion takeover of Alcoa.

Melbourne-based Alumina, Alcoa's 40 per cent partner in their Alcoa-managed global alumina alliance, Alcoa World Alumina & Chemicals, has been swept up in the speculation, rising another 11¢ yesterday to $7.34. Alumina told the stock exchange it had no information on the Alcoa takeover speculation and the "possible implications" that would have on its own future.

It also had no information on speculation that it could become the subject of a private equity bid.

Shares in Alcoa, the worst-performed of the major resources groups, rose $US2.10 to $US30.30 in the US market.

Analysts said investors were prepared to bet that Alcoa would be forced to break itself into an upstream business (bauxite, alumina and aluminium) and a downstream business (fabrication and extrusions) should no takeover bid emerge.

That would also be the plan of BHP and Rio, with the downstream operations to be offered up to any number of private equity buyers.