Standard Chartered's shares in Hong Kong tumbled to their lowest level in more than two and a half years on Tuesday, hit by broker downgrades following allegations by New York's financial regulator that the bank's US unit ran a "rogue institution" that "schemed" with Iran's government to hide illegal transactions.

At 06:00 GMT, Standard Chartered plunged 7% to HK$174.9, its lowest level since November 27, 2009, after its London-listed shares dropped 6% late Monday.