HONG KONG (AFP) - A Hong Kong inquest failed Saturday (Jan 9) to determine the cause of a student's death that fuelled tensions between protesters and the city's police force at the height of the pro-democracy rallies that swept across the financial hub in 2019.

A five-member jury at the coroner's court returned an open verdict, voting four to one, after a 29-day inquiry into the case of 22-year-old Alex Chow who died from head injuries following a fall from the third floor to the second floor of a car park near a protest.

Hong Kong was upended by more than seven months of pro-democracy protests in 2019 over moves by Beijing to tighten its grip on the city, and clashes escalated after Chow's death in November of that year.

"I want to tell my son that we have tried our best. Let's see if the truth will be revealed in the future," the student's father, Mr Chow Tak-ming, told reporters outside the court.

In delivering an open verdict, the jury determined that it could not pinpoint whether his death was an unlawful killing or an accident.

The events leading to his fall remain unclear and disputed. There were no witnesses or clear surveillance footage of the incident.

Chow's death - the first student fatality of the demonstrations - had further stirred protesters' anger towards the city's police as they alleged he was forced to jump because of tear gas rounds fired by officers during a clearance operation.

In late June last year, Beijing imposed a sweeping national security law in response to the 2019 protests, targeting acts it deems to be secession, subversion, terrorism and collusion with foreign forces.