SINGAPORE - The United States dollar is sliding against key Asian currencies as anxieties rise over results pouring in from the nail-biting US presidential election.

Democrat Hillary Clinton is now trailing Republican Donald Trump in the race for the presidency - she has 190 electoral college votes while he has 201. There are 538 electoral votes available and the winner needs 270.

The greenback weakened almost 4 per cent against the Japanese yen this morning - one US dollar could buy about 101.5 yen as at 11.30am, from 105.3 yen as at 9am.

The US currency has also been see-sawing against the Singapore dollar. One US dollar can now buy about S$1.387, down 0.3 per cent from a high of S$1.391 earlier this morning.

China's yuan firmed against the US dollar. Traders told Bloomberg the yuan market is closely following the move of the dollar, with the authorities seeking to control risks. The People's Bank of China set the midpoint rate at 6.7832 yuan per US dollar prior to market open, weaker than the previous fix at 6.7817 yuan. The spot market opened at 6.7846 yuan per dollar and was changing hands at 6.7711 at midday, putting the yuan 127 pips stronger than the previous late session close and 0.18 per cent stronger than the midpoint.

Meanwhile, Mexico's peso, which is seen as a proxy for Mr Trump's chances of becoming president, was in free-fall, diving nearly 10 per cent to a record low of 19.95 to the US dollar.

Commodities are also being hit. All industrial metals are sliding, and corn - a key US agricultural product - has fallen 1.8 per cent. Precious metals, however, are surging as investors flee to safety. Gold prices are up 3.4 per cent to US$1,315.

Analysts say markets are responding to a perceived shift in favour of Mr Trump.

Much attention is now focused on battleground states which have not reported numbers - Florida, New Hampshire, Pennsylvania and North Carolina.