The team on Friday heard accounts about ruptured eyeballs, broken bones and other serious injuries inflicted by police pellets or the impact of tear gas canisters.
"We are certain" that police have not respected their own guidelines about the appropriate use of force, said Dr. Enrique Morales of Chile's state Medical College.
Interior Minister Gonzalo Blumel has disputed such allegations, saying police were instructed "from the first moment" to follow protocols on ensuring public order and safety.
Authorities have also noted that at least 76 police officers have been injured in attacks by protesters.
At least 20 people have died in the protests, which started last month after the government announced a hike in subway fares. The protest movement expanded to include broader grievances over education, health services and growing economic inequality.
Most protests have been peaceful, but there have also been cases of arson and looting.
The mission sent by Michelle Bachelet, a former Chilean president who is the United Nations High Commissioner for Human Rights, is investigating allegations of human rights violations during Chile's unrest.
The United Nations team will collect testimonies and reports throughout the country. The team will continue its work until Nov. 22.
On Friday, about 100 people, including doctors and students, spoke for several minutes each to four members of the U.N. mission.
Morales, the doctor, said he and others displayed photographs of patients who had lost not only eyesight but also parts of eyeballs.
The Medical College says its doctors have treated more than 140 people for eye injuries, a statistic that does not include similar injuries recorded at private hospitals.
Chile's National Institute of Human Rights, which is independent of the government, has recorded 1,574 people who were taken to hospitals after being injured in protests. Several hundred of those were shot.
The institute has filed nearly 200 lawsuits against the state, including some related to alleged homicide and sexual assault.
In some cases, security forces have taken women to areas not monitored by security cameras and made them undress, according to María José Guerrero, head of a group called the Observatory against Street Harassment.
More protests are expected in Chile next week.