HONG KONG—Terri-Helen Gaynor has resigned as Asia-Pacific CEO at Burson-Marsteller, less than six months after taking on the role.

Gaynor, said the firm in a statement, is leaving for "personal and family reasons." She joined Burson at the start of this year, after a lengthy search to fill a position that had remained vacant for two years.

In her place, chief operating officer Margaret Key (pictured) has been promoted to Asia-Pacific CEO. Prema Sagar, principal and founder of Genesis Burson-Marsteller, takes on the additional title of regional vice chair, which was previously held by Burson's global vice chair and chief client officer Pat Ford.

Both Sagar and Key report to global CEO Don Baer. "Throughout Margaret’s two decades of experience in public relations, she has provided expert counsel to governments and multinational companies, while steadily taking on greater leadership responsibilities," said Baer. "I am extremely confident she will bring great talent to leading our continued growth throughout Asia-Pacific and to attracting and developing the brightest talent in the field."

Key had served as chief operating officer for Asia-Pacific for the past year and was acting Hong Kong market leader until earlier this year. She joined Burson-Marsteller in 2010 as Korea market leader, having previously served in senior roles at Edelman in Japan, Korea and Hong Kong.