"We tend to take the view that the least reliable statistics that come out of China are perhaps the GDP numbers, the unemployment numbers and the CPI numbers," Gambles told CNBC on Wednesday. Instead, investors should place more importance on data like energy usage, new car sales external Purchasing Managers' Index, which he said pointed to a less robust Chinese economy.

Earlier this week, David Carbon, Managing Director of Economics and Currencies at DBS Bank, told CNBC that China's economy is accelerating again,basing his argument on the latest inflation data, which came in at a higher-than-expected 3.6 percent in March.

But Gordon Chang, author of the book "The Coming Collapse of China", argued that inflation in China is under-reported, and has in fact fallen in recent months.

"I think one of the big stories is that the rate of inflation has obviously come down very, very quickly over the last three or four months, which shows a deterioration in the economy," Chang said. "When you put that together with the bad electricity production statistics, bellwether car sales, new lending, all of those numbers point to either a contraction or essentially an economy growing at 3 to 4 percent."

Chang added that China can’t be growing at 8.4 percent in the first quarter — as forecasted last week by Zhang Xiaoqiang, deputy director of China's National Development and Reform Commission.

"China's not going to grow at 8.4 percent. It grew in low-single digits in January and February, if you combine those two months, from any number of official statistics that the government issued. You'd have to have incredible growth in March, just to average out at 8.4," Chang said.

He also pointed to a contraction of the country's manufacturing sector, as reflected in the latest HSBC Purchasing Managers' Index (PMI) reading.

The HSBC private survey of smaller factories released earlier this month showed a reading of 48.3 in March, declining from February's 49.6, largely in line with a preliminary PMI reading of 48.1. The figures seem to contradict the official PMI, which jumped to an 11-month high of 53.1 in March, up from February's reading of 51.

Chang however cautioned against reading too much into the official figure, which measures the activity of large factories.

"It's an official number and that number doesn't correlate with anything that we know either about the January and February period or March," he said. "And when you look at the HSBC number, it's much more consistent with the data that we know."

Gambles added that the official PMI seemed weak given the strong factory activity expected after the Lunar New Year holidays.

"Following Chinese New Year, you always expect a strong bounce in PMI and actually the bounce in PMI wasn't so great even on the official numbers. Something like 56 would be more in line with the post-Chinese New Year PMI, so I think the problems are still there."

Their views are far more bearish than those of majority market watchers, who expect China’s full-year growth to exceed the 7.5 percent forecast by the Chinese government. Both Song Seng Wun, Regional Economist at CIMB Research, and Stephen Roach, a senior fellow at Yale University's Jackson Institute of Global Affairs, told CNBC earlier this week that China's economy could expand as much as 9 percent this year.