Moody's Investor Services, one of the world's big three ratings agencies, has downgraded the creditworthiness of China for the first time in almost 30 years.

Moody's is worried that the country's debt pile will rise at the same time as its economy continues to slow. It has also cut China's credit outlook to negative from stable, news that sparked an initial sell-off in Shanghai-listed stocks this morning. The impact on the China's tightly-controlled bond and FX markets was less pronounced, according to reports in The Wall Street Journal.