"Everyone who could leave did," said Liu, unwilling to give her first name. "It's only the poor who are left behind."

But Guangzhou's strained power network will notice little change, with the cement producer continuing to guzzle energy on the city outskirts even as residential districts are plunged into periodic darkness and factories forced on to night shifts.

Cement is one of several energy-intensive industries -- among them aluminium, steel and chemicals -- that are ratcheting up the environmental toll of China's breakneck industrial expansion through ravenous consumption of electricity from its mostly coal-fired plants.

China is often criticised for the amount of power it uses to generate each dollar of national income -- four times as much as the United States and nearly 12 times as much as Japan, the official Xinhua agency said.

Beijing has launched an efficiency drive to improve this figure, but as a developing nation where electrical appliances are still out of reach for many, power use on a per-person basis is far lower than these countries and some officials are starting to protest that China is taking the strain for other nations.

"We are producing some highly energy-intensive products in China on behalf of other countries," said researcher Jiang Xiaojun from a think tank attached to China's cabinet at a recent conference.

POWER-HUNGRY BOOM

As part of a boom based on cheap labour and tax breaks, China has drawn in energy-intensive industries such as aluminium, silicon, glass, paper, pulp and steel.

In 2004, it churned out more aluminium than any other nation -- accounting for almost 5 percent of all power used nationwide, or 99 gigawatt hours. It is also the world's top steel producer.

Overall, industrial users account for well over two-thirds of China's power consumption compared to just around a third in Britain.

These industries have been welcomed for bringing jobs and investment, but politicians are starting to worry about the cost to society and to other manufacturers forced to turn off machines or resort to expensive diesel generators when the power fails.

China last year faced its worst electricity crunch in two decades, and despite adding around 70 gigawatts of capacity this year -- roughly equivalent to Spain's entire generating plant -- the summer once more brought blackouts and power rationing to most of its major industrial centres.

And with over two-thirds of the country's power coming from coal-fired stations, they add to the smog that shrouds many of its cities and douses one third of its territory with acid rain.

China has seven of the world's 10 most-polluted cites, and according to the International Energy Agency, air pollution causes around 400,000 premature deaths.

But officials are starting to speak out. Lu Ming, a vice chairman of the Chinese People's Political Consultative Conference, a body that advises China's rubber-stamp parliament, recently warned against a foreign-funded silicon factory.

"The export-oriented factory would not only nibble at China's scarce silicon reserves but also increase the power transmitting pressure on power-generating bases in Sichuan and Shanxi Provinces," Xinhua quoted Lu saying in an article airing concerns China was becoming a "haven" for energy-intensive sectors.

FIGHTING JOBLESSNESS

Many plants are supported by the financial interests of local officials, or are big employers in areas with few other options.

The government, wary of social unrest as China's wealth gap widens, seems often prepared to put up with the energy inefficiency and pollution to stave off joblessness.

"Frankly it's quite difficult for the government to sacrifice a significant amount of its economic growth for environmental levels that North America and Europe only achieved recently," said Chris Raczkowski, managing director of renewable technology firm Azure International.

However, energy-intensive industries are not an efficient way to combat poverty -- an auto factory employs 100 times more people than an aluminium smelter using the same amount of power.

And industrial pollution may create the very instability growth is intended to fend off. In late July hundreds of rioting farmers forced a pharmaceutical plant to close because chemical waste was polluting their river and ruining their crops.