1236 GMT February 24, 2020
Luo Huining replaced Wang Zhimin as the head of Hong Kong Liaison Office, AFP reported.
The 65-year-old Luo delivered a short statement to reporters.
"In the past six months, Hong Kong's situation has made everybody's heart wrench. Everyone earnestly hopes that Hong Kong can return to the right path," Luo said.
Millions have come out on the streets since June last year in a wave of protests sparked by opposition to a now-abandoned proposal to allow extraditions to mainland China.
While the huge protest marches have been largely peaceful, smaller groups of hardline protesters have repeatedly battled riot police.
Luo said Hong Kong had made an "important contribution to (China's) opening up and modernization."
He quoted President Xi Jinping's New Year speech saying "without a harmonious and stable environment, how can there be a home where people can live and work happily."
The director of the Liaison Office is the highest-ranking Chinese political official in Hong Kong.
Luo previously served as governor of Qinghai Province, and was also appointed to senior Communist Party positions in Qinghai and Shanxi provinces, according to state-run China Daily.