SEOUL: South Korea's central bank is suspected to have sold around $1 billion on Friday to stem a rapid fall by the country's currency, three currency dealers said after onshore trading ended.

The won dropped as low as 1,182.9 per dollar at midday, its weakest since January 2017, prompting the Bank of Korea to sell dollars to stem a further drop, the dealers said.

"Authorities started to intervene in the market after the won reached the year's low, especially in the afternoon," said a dealer who insisted on anonymity.

The won has fallen about 5.3 percent against the dollar this year, making it Asia's worst performing currency.