SHENYANG, China, March 11 (Reuters) – In a tunnel deep beneath Shenyang's busy streets, Lu Ze flicked a switch and a lone light bulb revealed a cluttered concrete floor.In a tunnel deep beneath Shenyang's busy streets, Lu Ze flicked a switch and a lone light bulb revealed a cluttered concrete floor.

Electric wires and metal pipes lay in a jumble. Tiles dangled from the ceiling. Dust hung heavily in the air.

But Lu, a construction supervisor, was supremely confident that a train would be gliding past the very same spot by October, the first of 11 metro lines planned in this rustbelt city in northeastern China.

''We've been working nearly every day for the past year and we will have it done on schedule. Then we'll get a month off and come back to work on the second line,'' he said with a weary grin.

Shenyang's ambitions are vast in scale and yet commonplace in China. More than 30 cities have started building or have submitted proposals for entirely new metros. The five cities with existing systems are expanding them. And all of this is just part of a larger investment frenzy in railways, airports and roads.

The stakes could not be higher.

Managed well, the infrastructure boom will bestow on China the hardware to power its growth for decades to come. Managed poorly, money will be squandered, leaving the country with bridges to nowhere and a hefty bill.

But China has not become the world's fastest-growing economy by dragging its feet. Things tend to move quickly once the government throws its weight behind big projects.

''You solicit views, you apply for approval and then you just do it,'' Zhang Zhenbang, vice general director of Shenyang Metro. ''London needed more than a hundred years to build up its metro, but we'll need less than half that in China.''

When exports collapsed last year due to the global financial crisis, China turned to infrastructure to make up the shortfall.

It built and expanded 35 airports, opened 5,557 kms (3,453 miles) of railways, including the world's fastest high-speed line, paved 98,000 kms of highways and, of course, ramped up work on metros from Shenyang in the north to Guangzhou in the south.

Overall, gross capital formation – the best indicator of infrastructure spending – accounted for 8 percentage points of the economy's 8.7 percent growth last year.

The headlong rush to build, build, build has inspired a heated debate among China-focused economists about whether the government is simply overdoing it.

Michael Pettis, a senior associate at the Carnegie Endowment for International Peace in Beijing, is adamant that China already has the world's best infrastructure for its level of development. Investing too much now suppresses the household spending that is badly needed to prop up a hobbled global economy.

''The growth in Chinese consumption will necessarily be limited by the growth in Chinese household income, and Chinese household income cannot grow quickly enough if they are forced to pay for infrastructure that's not economically justified,'' he recently wrote.

Yet others think that the better benchmark is not countries at China's current stage of development, but those it is quickly catching up to. Chinese rail density is, for example, only 40 percent of the US level and 11 percent of Japan's.

Qing Wang, an economist at Morgan Stanley, noted that China's rate of return on capital – a basic measure of investment efficiency – far outstrips that of most advanced countries.

''We would argue that claiming 'over-investment' in China simply based on the pace of investment growth is equivalent to making the observation that 'a person must be overweight because he seems to be eating a lot,'' Wang wrote in a research note.

''A hearty appetite reflecting a fast metabolism is a sign of health and vitality.''

In Shenyang, at least, the rationale for building a metro is clear enough. Japanese occupiers in World War Two had planned a four-line metro system when the city was home to just over 1 million people.