Footage posted on social media on Thursday night showed Hong Kong Justice Secretary Teresa Cheng fall to the ground while being pursued by a large group of anti-Government protesters in the British capital.
The Hong Kong Government claimed the incident caused Ms Cheng “serious bodily harm” while China said she injured her hand.
Both accused demonstrators of attacking her, but protesters at the scene claimed she tripped and that the incident had been exaggerated for political reasons.
The Metropolitan Police said she had been taken to hospital by ambulance for treatment, adding that it was investigating an allegation of assault.
No arrests had yet been made, the force said.
Warning: The footage in the tweet below contains flash photography
Ms Cheng was in the UK to give a seminar at the Chartered Institute of Arbitration on Thursday and was departing when the crowd followed her, shouting and appearing to point a flashing light at her as she passed.
Demonstrators said they targeted the official due to her role in legal proceedings against protesters in Hong Kong and her support of the controversial extradition bill – cancelled legislation which would have allowed some criminal suspects to be sent to mainland China.
Protesters said Ms Cheng also played a role in disqualifying pro-democracy activist Joshua Wong from running in Hong Kong council elections and is “thus a key culprit of destroying the rule of law”.
“HongKongers of course took the opportunity to protest,” a demonstrator, who asked to remain anonymous, told PA.
“It was small scale and people were chasing after her and yelling at her, and amidst chaos, she did trip over.
“Now, the HK Government is calling the protesters violent mob and radicals, reporting the case to Met Police, making it pretty big.”
The Chinese embassy said in a statement: “We express strong indignation and unequivocally condemn the activists.
"Now, they are taking such violence abroad and into the UK."