The situation may be even worse than China's official statistics, according to many analysts.
"The Chinese published GDP figure is absolutely garbage," said Leland Miller, CEO of China Beige Bok advisory firm. "There is absolutely agreement that these numbers are unreliable."
Some experts suspect that China's chief statistics, which report much of the country's data, are more focused on making the government look good rather than providing an accurate reflection of its financial health.
It is difficult to determine China's true growth rate, as many government data "do not make sense", according to Saks, who is also c hief economist at China Beige Book. For example, the figures on the size of the economy relative to the average income of Chinese citizens do not match, he said.
Many other analysts take their own calculations to get a feel for how the economy does.
Research company Capital Economics examines a number of data, including sea freight, electricity generation and financial lending, to come up with a proxy indicator. Based on that, China's economy could only have grown by around 5% last year instead of the official 6.6%.
The slowdown has thrown gloomy over Chinese businesses.
"The economy will get worse in the coming months," said Wei Bingyu, the owner of an industrial paint factory in Beijing. He blamed the difficulties on trade war and other issues.
Chinese consumers feel pressured
Official Chinese data is probably "excessive consumption growth," Julian Evans-Pritchard, senior Chinese economist at Capital Economics, said in a recent note to clients. He estimated that spending in China's large urban areas was reduced by about 3% last year, suggesting that medium-sized buyers are tightening their belts.
It counts with what some business owners say. Zhou Chang, the owner of a gym in central Beijing, told CNN that his customers are using less.
Using a gym "is not quite like eating, clothing, housing or commuting," Zhou said. "They are must-have while bodybuilding is not." As the economy slows down "many gyms have temporarily closed or gone bankrupt," he added.