Here are 2 threats to Hong Kong's credit rating

Moody's assigns Aa1 rating to government bonds.

According to Moody's Investor Service, Hong Kong's rating carries a positive outlook, as does China's rating. However, 1) a narrow and volatile government revenue base, and 2) increasingly high concentration of trade and investment with the rest of China remain its 2 key threats.

Here's more:

Hong Kong's Aa1 government bond rating reflects the Special Administrative Region's very high economic resiliency, very high government financial strength, and some susceptibility to event risk.

Economic resiliency is demonstrated by the very strong economy, with very high per capita income and competitiveness in a number of areas, including financial services and international trade.

In addition, Hong Kong's institutions are very strong in the areas of governance, rule of law, and transparency. As a result, Moody's is of the opinion that the SAR has a high degree of economic resiliency.

The SAR's fiscal and external indicators have strengthened over the past several years, and Moody's believes that Hong Kong's government finances are among the strongest in the world.

As Hong Kong's banks are, on average, strong, the likelihood of any major infusion of capital into the banking system appears limited, despite the establishment of a facility to enable this at the time of the global financial crisis.

The outlook for government financial strength and the external asset position of the SAR is for further strengthening.

What Could Change the Rating - Up
Hong Kong's rating could move up if China's rating were to be upgraded, a possibility given the positive outlook on China's rating. A move upward in HK's ratings would also be contingent on continued government financial strength and a strong external asset position.

What Could Change the Rating - Down
The rating could come under downward pressure should there be a loss of confidence on the part of investors that led to capital outflows and weakened external and fiscal positions.

While this seems unlikely, such a scenario could conceivably develop if the exchange rate regime were to come under pressure or was changed in a way that did not maintain investor confidence.

Instability in China that led to a deterioration in China's credit standing could also affect HK's ratings.