It is the first time in WHO's history that a regional director has been dismissed.
The Associated Press reports an email sent to employees on Wednesday by WHO Director-General Tedros Adhanom Ghebreyesus said Dr Takeshi Kasai's appointment had been "terminated" after an internal investigation resulted in "findings of misconduct".
A summary of the internal WHO investigation found Dr Kasai regularly harassed workers in Asia, including engaging in "aggressive communication, public humiliation, [and] making racial comments."
The director-general said the process of finding a new regional director would begin next month and be finalised in October.
Dr Zsuzsanna Jakab has been appointed acting regional director for the Western Pacific.
She has served as WHO deputy director-general since 2019 after serving as WHO regional director for Europe from 2010-2019.
The WHO website said Jakab has held a number of high-profile national and international public health policy positions in the last three decades, including as the founding director of the European Centre for Disease Prevention and Control.
The Western Pacific covers a vast area from Mongolia in central Asia, east to the Pitcairn Islands and south to New Zealand.
WHO’s Western Pacific Regional Director Dr Takeshi Kasai addressing Parliamentarians on the health impacts of a changing climate. Photo: Supplied/ Infinity Images Fiji