Also, the desire of pension-fund managers to buy long-term assets to match their payout commitments has led them into most parts of the credit market.

Market spreads taking account of credit and liquidity risk had arguably become too compressed pre-August 2007, and are now wider than they should be long-term.

Analysts say the downgrading of the US long-term sovereign credit rating may lead to a weaker US dollar, which may bring a negative impact onto China's export market as well as imported inflation.