When two of China's most influential government policy think tanks highlight the risk that growth will weaken on the same day that a widely-watched indicator fails to signal an expected upturn, investors are naturally nervous.

The question is whether a warning by the cabinet's Development Research Centre of the need to prepare for "extreme risks", a State Information Centre assessment growth is slowing faster than thought and a slip in a private sector survey of factory activity signal a significant shift in the economy.

Adding in a risk-laden assessment from a third government think tank in 24 hours suggest at the very least that investors should be erring on the side of caution given that growth has slowed for four successive quarters and almost certainty slowed again for a fifth.

"If the government does not intervene and accelerate policy easing, growth will continue to slow," is the blunt assessment of Wang Jun, an economist at China Centre for International Economic Exchanges (CCIEE).

He told Reuters his first-quarter growth forecast had been cut to around 8 percent from 8.5 percent.

Wang's call echoes that of Zhu Baoliang, chief economist at the State Information Centre. He told Reuters he had trimmed his first quarter call to 8.2-8.3 percent from 8.5 percent and cautioned growth could slip below 8 percent if the central bank failed to unveil more policy easing.

For those paying close attention to the shrinking government growth forecasts and steady refrain of China's top leadership for the last 18 months that a structural slowdown to growth is inevitable - and desirable - then this is just reality biting.

China has long said structural changes in its economy, from demographics to investment and rebalancing to more consumer-led, domestic demand are damping down headline growth from three decades of roughly double-digit annual expansion.

The issue for investors is the extent to which the government has the policy flexibility to add extra impetus to slowing growth in the face of a deeper downturn than anticipated in external demand owing to the euro area debt crisis and a sluggish U.S. economy, while internal economic change is accommodated and whether it really signals the need for a more urgent or outsized monetary and fiscal response.

"Yes, there's a slowdown. The question is how big is that slowdown?" Ting Lu, China economist at Bank of America/Merrill Lynch in Hong Kong said.

"If I'm an economist for the government, I've got to tell them to be worried about this and to do this and do that," Lu said. "There's an element of policy persuasion in their work."

Core assumptions

There's doubtless an element of persuasion in the investment bank view of the world too, though both seem to be gravitating around core assumptions - more policy action is required to keep growth on track and the economy should expand a little over 8 percent in first quarter and around 8.5 percent for the year.

Both numbers are way above official government guidelines. China's 12th five-year plan assumes growth will average 7 percent over 2011-2015. The official 2012 target announced three weeks ago by Premier Wen Jiabao is 7.5 percent.

If Wen's targets are the minimum acceptable, the economy is on course to exceed expectations, especially if a rebound anticipated in the second half of the year comes good.

A handful of investment banks have recently upgraded their China growth forecasts, including UBS and Nomura, though only by enough to bring them more into line with prevailing consensus.

Data in the first two months of the year, smoothed to take into account the Lunar New Year distortions to output and investment, gave Nomura's chief China economist, Zhang Zhiwei, the impetus to upgrade his growth call. At 8.2 percent for 2012, though, he is still tilted towards the bearish side.

He says the downside surprise in Thursday's HSBC flash manufacturing purchasing managers index (PMI) for March, which showed factory activity shrinking for a fifth straight month, justifies caution.

"The consensus for GDP growth is still about 8.5 percent and that's still a bit optimistic for me. For the first quarter we think GDP will be below 8 percent, so it's too optimistic to expect such a big recovery in the second half," Zhang said.