Police officers killed at least 3,345 people in 2015 in Brazil, according to the latest available data, said the nonprofit human rights organization.
"Torture and extrajudicial killings by police contribute to a cycle of violence in Brazil, undermining public security and endangering the lives of police officers," the US-based HRW said in its 2017 world report.
Police officers killed at least 3,345 people in 2015 in Brazil, according to the latest available data, said the nonprofit human rights organization. That reflected a six percent rise from 2014 and a 52 percent surge from 2013.
"While some police killings result from legitimate use of force, others are extrajudicial executions," HRW said.
The violence is scaring off citizens from cooperating with the police to help catch criminals, it warned.
It also said "inhumane conditions in prisons and detention centers is an urgent problem" in Brazil.
Around 100 inmates were killed last week, some of them beheaded and dismembered, in a series of prison massacres blamed on drug gangs.
Brazilian prisons are packed with 67 percent more inmates than they are designed to hold, HRW said, citing official data.
"Overcrowding and understaffing make it impossible for prison authorities to maintain control within many facilities, leaving detainees vulnerable to violence and gang activity," it said.
"Torture and mistreatment of detainees, including children, is an acute problem."
President Michel Temer has said the government will spend $250 million to build at least one new prison in each of Brazil's 26 states.
The HRW report also said Brazilian authorities should "provide better support for the families with children diagnosed with Zika syndrome."
Thousands of families are struggling to look after babies born with brain damage due to last year's outbreak of the mosquito-borne Zika virus.