Thousands of Hong Kongers formed long lines to attend a memorial service on Thursday for a student whose death led to some of the most violent clashes in six months of democracy protests.

Alex Chow, 22, died last month from head injuries sustained during a fall inside a multi-storey carpark where police and protesters were clashing.

Although the precise chain of events leading to his fatal accident is unclear and disputed, protesters have made alleged police brutality one of their movement's rallying cries.

Chow's death was followed three days later by police shooting an unarmed 21-year-old protester in the abdomen sparking days of political unrest that culminated in pitched battles on university campuses.

Mourners arrive to pay their respects at a memorial service for Hong Kong student Alex Chow, 22
Mourners arrive to pay their respects at a memorial service for Hong Kong student Alex Chow, 22 AFP / Anthony WALLACE

The last three weeks have seen a rare lull in the violence and vandalism after pro-democracy parties won a landslide in local council elections.

Huge crowds marched last Sunday for a rally that ended without a single tear gas canister being fired.

But Beijing and city leader Carrie Lam have shown no sign they are willing to make further concessions, leading to fears clashes could resume.

Emotions were running high outside the venue where Chow's memorial service was taking place on Thursday evening as people formed snaking lines and queued for hours.

"There are so many suspicious elements and I hope he can finally rest in peace when truth is found," Joe Cheung, an 18-year-old student, told AFP.

Long queues formed for people to pay respects
Long queues formed for people to pay respects AFP / Anthony WALLACE

Media were not allowed inside the venue. But a teacher who attended with her son and gave her first name Macy, said the memorial hall was decorated with white flowers and photos of Chow.

Above his main picture, there was a banner with the Chinese characters saying "Rest in God's arms", she said.

"It was simple and made you feel calm and peaceful," she said.

Cantonese pop star Denise Ho, whose music is banned on the Chinese mainland, and veteran Catholic Cardinal Joseph Zen were among the city's high profile democracy supporters who attended, AFP reporters at the scene said.

Noticeboards said Chow's funeral would take place on Friday morning and colourful bouquets lined the entrance.

Police have repeatedly denied any allegations of wrongdoing in relation to Chow's death, saying officers were not near the spot when he fell.

Protests have rocked Hong Kong for more than six months, with up to two million people taking to the streets, initially against a now-shelved extradition bill.

Latterly, one of the core demands of protesters -- alongside fully free elections -- has been an inquiry into the police, who have been left to battle increasingly violent black-clad activists and are now loathed by significant chunks of the deeply polarised population.