The S&P 500, an index of US companies, has fallen below 1900 points for the first time since September.
The index, which entered the new year over 2000, has fallen victim to a global rout in equity prices that has been triggered by volatility in Chinese financial markets. It is currently down 2.31 per cent on the day at 1893.92.
Among the day's biggest fallers are a host of energy companies, suggesting the fall is also due to fears over the price of oil. West Texas Intermediate crude – a US benchmark – fell below $30 a barrel yesterday for the first time since 2003.
The S&P 500 hit a record high of 2134.72 last year.