Detectives are looking into the death of a suspected triad member who passed out and died after he allegedly assaulted an off-duty policeman onboard a minibus in Tsuen Wan on Wednesday.
The alleged assault took place when the minibus was travelling on Tak Wah Street near Yan Chai Hospital at about 8.30pm.
The suspected triad member, a 30-year-old man, had claimed that his mobile phone had been stolen.
He was then accused of assaulting a 42-year-old passenger, an off-duty police sergeant, onboard the minibus, according to police.
The 43-year-old minibus driver pulled his vehicle over during the incident.
"[Tsang] was subdued by the victim and other passengers before officers arrived," a police spokeswoman said.
The man was then arrested and handcuffed when police arrived at the scene.
Police said the man was later found to have passed out, but no external injuries were found on him.
He was taken unconscious to Yan Chai Hospital in the vicinity, where he was declared dead.
The Fire Services Department said it received a call from police requesting an ambulance at about 9pm on Wednesday.
An ambulance arrived at Tak Wah Street at 9.07pm.
It left the scene at 9.19pm and arrived at Yan Chai Hospital within two minutes, the department said.
The off-duty police sergeant, who suffered an injury to his nose, was also treated at Yan Chai Hospital.
Police are treating the case as suspected wounding and death of a person in custody.
Crime-squad officers from the New Territories South regional crime unit are investigating the matter.
A police source said Tsang was a suspected triad member as well as a drug abuser.
It was understood that the man appeared to be in a dazed state before the alleged assault took place.