The global aluminium production sector is becoming ever more polarised.

China's national output of the light metal has risen by 3.36 million tonnes annualised since the first quarter of this year, while output in the rest of the world has contracted by 1.06 million tonnes over the same period.

China is now within a whisker of producing half of the world's aluminium output. Average daily production in November was 65,130 tonnes, according to the China Nonferrous Metals Industry Association. Production in the rest of the world was 65,630 tonnes, according to the International Aluminium Institute (IAI).

It may have already got to the 50 per cent mark. Both agencies include an estimate for unreported production and for China that is currently 200,000 tonnes per month, while for the rest of the world it is 65,000 tonnes.

If it hasn't, it's probably only a matter of time since the increasingly divergent production trends show no signs of stopping. Outside China the world of aluminium smelting is characterised by high stocks, low prices and producer pain.

Producers have announced cutbacks of about 1.2 million tonnes this year. November production fell to an annualised 23.94 million tonnes, the lowest run-rate since February 2010, when output was still recovering from the financial crisis.

However, not all of those cutbacks have yet shown up in the IAI figures to the end of November. Included in the net 1.06 million tonne decline since March is one non-price related outage, namely a 370,000-tonne per year potline at the new Ma'aden smelter in Saudi Arabia. Alcoa, which operates the plant in a joint venture with Saudi Arabian Mining, said in October it halted the line after "a period of pot instability" during the commissioning process.

It said it would accelerate the commissioning of a second potline; but the overall impact on the plant's output and timeline to full operation is unclear.

However, it is noticeable that annualised production in the IAI's Gulf category has dropped sharply by just over 200,000 tonnes annualised over the course of October and November.

The implication is that production elsewhere has a bit further to fall as targeted high-cost smelters continue to ramp-down, particularly in North America and Russia, where the curtailments are concentrated.

China is not immune from the same price and margin pressures affecting producers everywhere else. Older capacity has been closed, though probably not by as much as it should have been, given local governments' habit of subsidising loss-making plants.

The real game-changer this year, however, has been the ramp-up of greenfield capacity in the country's northwestern provinces, particularly Xinjiang, where a new generation of smelters using trapped coal reserves as a cheap power source is pushing national production ever higher.

Along with steel, aluminium is a regular on Beijing's list of bloated industries, blighted by overcapacity and in need of restructuring.

The latest salvo in the long-running battle between central and regional governments was fired in October, when the State Council issued a new plan, promising to focus on "establishing and perfecting" market mechanisms to rein in recalcitrant sectors.

There are already reports of tougher environmental constraints on the steel sector, particularly on mills near smog-plagued Beijing.

Any impact on the country's aluminium sector, though, seems so far negligible, given the strength of the upward trend in production over the last few months. The real Achilles' heel of the smelter sector is its reliance on imports of bauxite, particularly Indonesian bauxite.

That country's pending ban on exports of unprocessed minerals might pose some risk of disruption to affected Chinese smelters, but probably not any time soon.

The current consensus is that Chinese buyers have built up stocks before the January 15 deadline and have also started looking elsewhere, particularly Australia, India and Guinea, for alternative supplies.

China is also the fastest-growing user of aluminium and so far at least any over-production is largely staying in China. At least in terms of primary metal.

The country is still a marginal net importer, largely thanks to a prohibitive 15-per cent export tax and to preferential tax treatment for operators tolling imported metal into products.