Well, China once was the biggest world's economy. Only in the 1880's it was overtaken by the US. A prolonged period of bad government depressed the size of China's economy in relative and absolute terms. Only recently, China has increased to a size it would have without the horrors of Mao's 'Cultural Revolution' and the backwardness of the imperial era.
China has grown rather rapidly since the early 2000's. This is why:
China's credit volume has grown in relative as well as absolute terms. However, no tree grows to the sky. Even China has its limits. The sheer size of debt is one of them. The following chart shows that Chinese economic growth has required an ever faster pace of credit growth. This is simply not sustainable.