Shares in HSBC plunged amid frenetic trading in Hong Kong on Monday to touch a 13-year low, as short sellers tried to profit from the British bank’s $17.7bn (£12.6bn) rights issue and rating agency Moody’s produced a gloomy outlook.

After the close, Moody’s Investors Service downgraded the bank’s long-term deposit and debt ratings of its US division, citing pressures on the unit’s capital position.