The Singapore Post sign at a post office in Singapore November 2, 2015.

Singapore Post said on Sunday it had dismissed its chief executive and two other senior managers after an internal investigation found they had mishandled whistleblower allegations about misconduct by company employees.

The firm's shares slumped by the most in over four years as the city-state's bourse opened for trading. The stock plunged as much as 9.8%, its biggest intraday loss since March 2020.

The alleged misconduct reported by the whistleblower related to several employees who worked in the company's international e-commerce logistics parcels business, the company said in a statement, without giving further details.

The firm had received a whistleblowing report alleging that three unnamed employees had either approved or manually updated a "delivery failure" status code for parcels, even though no delivery was done, the statement said.