Protesters on Sunday threw bottles, stones and Molotov cocktails at the façade of the police headquarters, while a crowd of around 30 stormed the building, Poland’s PAP news agency reported.
In response, police tear-gassed the crowd and detained 30 of the most aggressive protesters, according to officials.
The incident occurred after local police on Friday morning detained a man that they said behaved in an aggressive manner.
A video footage that went viral showed four officers trying to subdue the man and put him in a police vehicle. In the video, the man tries to break free, screams and calls for help. At some point he loses consciousness.
Officers say they were responding to an emergency call from the man's mother, who said her son had been using drugs and behaving violently.
The Provincial Police Department in Wrocław, southwestern Poland, said in a statement on Saturday that, "considering the man's aggressive behaviour and reasonable suspicion that he may be under the influence of drugs,” more officers were called to the site “to prevent an escalation.”
An ambulance with a team of paramedics was also deployed, the force said.
The man died two hours after being taken to the hospital, according to the police statement.
A lawmaker from Poland's main opposition grouping, the Civic Coalition (KO), Piotr Borys, has challenged the police version of the events, saying it is “not true,” the PAP news agency reported.
“According to information from the hospital management, the young citizen of Lubin died in the ambulance before it arrived at the hospital,” Borys wrote on Twitter.
Prosecutors have launched an investigation into the incident, officials told reporters.