Keep Australia Australian is the rallying cry of the Senate opposition leader Barnaby Joyce's TV ads against China's proposed $19.5bn (£13.9bn) investment in Rio Tinto, the Anglo-Australian miner.

Mr Joyce is not only the latest to join the fracas over the Rio deal, he also joins a swelling choir of concern that China is exploiting the global economic downturn to buy up the West. Beijing's growing shopping list is not a masterplan for political expansion but an attempt to secure the country's supply of raw materials and avoid looming social unrest.

Mr Joyce's concern is that the deal with Chinalco, the state-owned aluminium giant, will leave an Australian "source of wealth" in foreign hands. "The Australian government would never be allowed to buy a mine in China, so why would we allow the Chinese government to buy and control a strategic asset in our country?" he said.

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The Middle Kingdom's sway over commodities markets is already profound. It was Chinese hunger for the raw materials needed to fuel its run of double-digit annual growth that sent prices through the roof. It is the slowdown in China that has sent prices crashing and industries from mining to shipping into reverse gear.

Mr Joyce's concerns are not restricted to Rio. He is also campaigning against the proposal for China's Minmetals to buy debt-laden Oz Minerals, the world's second largest zinc miner, for A$2.6bn (£1.2bn). Neither does the acquisition trail end there. As miners struggle, China's investments are becoming a spree. In early February, Zhongjin, its third-largest zinc producer, bought a controlling stake in Perilya, a medium-sized zinc and lead producer, for A$45.5m. The following week, Hunan Valin Iron & Steel picked up a 16.5 per cent stake in Fortescue, Australia's third-largest iron ore producer, for $771m.

The Fortescue deal was swiftly followed by the China National Petroleum Corporation's cash offer for Verenex Energy, a Canadian group with resources in Libya. Then, early this month, Sinosteel bought nearly 6 per cent of Murchison, the iron ore miner, to add to its purchase of Midwest, a rival, last year.

There is no doubt that China is taking advantage of the downturn. Jonathan Fenby, the director of China research at Trusted Sources, said: "It clearly sees a promising opportunity in the raw materials field in which it can benefit from its cash pile at a time when companies abroad need money or asset prices are cheap."

But this is no stealth mission. At a National Energy Administration conference in Beijing last month, government officials openly admitted they are considering creating a special fund for buying foreign oil and gas companies. Neither are the acquisitions indiscriminate. Reports that Chery Automobile, the local car maker, is interested in Volvo receive short shrift from experts.

"It looks as though Western firms would welcome a Chinese approach in the car industry but there is not much industrial logic on their side," said Mr Fenby. "China has overcapacity at home in vehicle production and its prime aim is to get the domestic industry into shape."

China did make a brief foray into Western financial institutions, spending $3bn on Blackstone and $2.2bn on Barclays at the height of the market in 2007. But the credit crunch left massive paper losses on the deals, and not only did Beijing show no interest in rescuing collapsing banks but China Life recently pulled out of the bidding for the AIG's Asian arm over worries about the quality of the business. Robin Geffen, the managing director of Neptune Investment Management, said: "China is simply not interested in taking over Western companies, only in securing supplies of what it deems vital natural resources."

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Two gargantuan loans agreed last month in return for guaranteed delivery of oil at the market price do not look like the actions of an empire-builder. Just days after the Minmetals deal, Sinopec stumped up a $10bn for Petrobras, the Brazilian oil company, in return for 100,000 barrels of oil per day (bpd) for the next 10 years. The same week, China Development Bank also agreed to lend a whopping $15bn to Rosneft, the Russian state oil company, and another $10bn to Transneft, the pipeline operator, in return for 300,000 bpd delivered for two decades.

"The most significant of all the recent deals is the one with Russia," said Mr Geffen. "China could buy every bank in Europe with the $25bn being leant to the Russians, but it chose not to."

Chinese investment overseas is not new. The government has spent billions of dollars on natural resources concessions in Africa in recent years, raising similar spectres of shifting geopolitical influence as are the current save of acquisitions. But Beijing has repeatedly rejected calls for it to take a more interventionist role on the global stage and remains focused on its domestic concerns, says Mark Ashurst, the director of the Africa Research Institute.

"Only a government that came to power through rural unrest can understand the implications of lifting millions out of poverty while leaving millions more behind," said Mr Ashurst. "China is not interested in changing the world order, only in securing long-term, strategic concessions which will bring energy security for the industry back home. The Communist Party is a fragile regime: providing energy, industry and jobs to its own citizens is the priority."

Into Africa: China's interests stretch from Angola to Sudan

China's shopping list of international miners follows years of investment in Africa in return for the guaranteed supply of raw materials.

To the chagrin of the West, China's pragmatic approach has proved highly successful. The formula is simple: in return for long-term concessions for key strategic resources such as oil, gas and metals – sometimes for hundreds of years – Beijing agrees premium prices for the products and to make massive infrastructure investments.

There is no shortage of takers – China has oil interests in Angola, Sudan and Nigeria, and mining concessions across the Democratic Republic of Congo (DRC) and neighbouring Zambia. As part of the package it is funding rail programmes from DRC to Dar es Salaam in Tanzania, and inland from the port of Benguela in Angola. Alongside state infrastructure like rail and road networks, Beijing can also be prevailed upon for politically useful building programmes like hospitals.

Part of the appeal is money. China is cash-rich and will pay whatever it takes for the energy security it craves. It is also not at all squeamish. When the Western banks providing Angola's annual syndicated loans came under pressure to add transparency criteria to their terms, Chinese institutions stepped in and took over with no questions asked. Similarly, China is widely accused of handing over tens of millions of dollars to at least one African leader in return for repudiation of Taiwan at the UN, although nothing has ever been proved.

"China will undertake these big infrastructure projects in places where nobody else will, and will get them built very much quicker than if they were relying on cumbersome development aid coming from the West," said Mark Ashurst, the director of the Africa Research Institute. "China has a simple proposition which is attractive to African leaders, and if sweeteners are needed then there are plenty available. It is not particularly clean, but it is very rational."