President Barack Obama says the whole country should be troubled, that the shootings are not isolated incidents and are symptomatic of racial disparities in the justice system.
The aftermath of the latest death was live-streamed on the internet by the victim's girlfriend as her young daughter watched.
Philando Castile had been pulled over in suburban Minneapolis because of a broken rear light and was allegedly reaching for his licence when an officer opened fire.
"Oh, my God, please don't tell me he's dead. Please don't tell me my boyfriend just went like that."
(Officer:) "Keep your hands where they are, please."
"Yes, I will, sir. I'll keep my hands where they are."
That is the voice of Diamond Reynolds, just moments after watching a police officer repeatedly shoot her boyfriend, Philando Castile.
Her mobile phone is not just capturing the immediate aftermath of the United States' latest police shooting, but streaming it live on Facebook.
At the window, an officer is pointing a gun into the car.
Next to Ms Reynolds is her blood-soaked boyfriend, quickly losing consciousness.
Watching it all unfold from the back seat is her four-year-old daughter as Ms Reynolds continues talking as if in shock.
"Please, Officer, don't tell me that you just did this to him. You shot four bullets into him, sir. He was just getting his licence and registration, sir."
The 32 year-old Mr Castile had been pulled over because one of his rear lights was not working.
He apparently told the officer he had a legally purchased, concealed weapon with him.
His girlfriend says, when he reached for his documentation, the officer opened fire.
Mr Castile was taken to hospital, where he was declared dead.
Ms Reynolds continued live-streaming from her phone after being arrested.
"I don't know if he's okay or if he's not okay. I'm in the back seat of a police car."
Protesters gathered outside the home of the Minnesota state governor throughout the night, draping it with yellow police tape taken from the scene of the shooting.
After being released by police, Diamond Reynolds joined them, appealing for justice and paying tribute to Mr Castile, who had worked as a cafeteria supervisor at a local school.
"He was never a bad man. He never did anything to hurt anyone. He was the quietest, most laid-back person you will ever meet. He was loving. So even for the police to take him away, nothing within his body language said intimidation, nothing within his body said, 'Shoot me,' nothing within his body language said, 'Kill me, I want to be dead.'"
Philando Castile's mother Valerie says she believes her son was killed because he was black and in the wrong place.
"They're still saying there's no profiling, but it is. It is. We're being hunted, every day. It's a silent war against African-American people as a whole."
Two days earlier, police shot dead a man in the state of Louisiana.
After the Minneapolis shooting, President Barack Obama says the country has seen such tragedies too many times.
Speaking from Poland, he says this week's shootings are not isolated incidents but symptomatic of a broader set of racial disparities existing in the US justice system.
"When incidents like this occur, there's a big chunk of our fellow citizenry that feels as if, because of the colour of their skin, they are not being treated the same. And that hurts. And that should trouble all of us."
Minnesota governor Mark Dayton has requested a federal investigation into the incident.
He said he does not think the shooting would have happened if Philando Castile and his passengers were white.
Governor Dayton has asked the people in his state to confront racism.
"Philando was not given first aid. Nobody attended to his condition, as they were attending to the condition of the police officer who did the shooting. She (Ms Reynolds) was handcuffed and taken to a station, police station, with her four year-old daughter. Just the stark treatment, I find absolutely appalling."
In the earlier shooting in Baton Rouge, Louisiana, video shows 37 year-old Alton Sterling being held down by two white police officers before being fired on several times.
That sparked protests and an outcry on social media, including a video uploaded on Facebook by outraged black policewoman Nakia Jones.
"How dare you stand next to me in the same uniform and murder somebody! I wanted to quit when I saw that video. But I need for y'all to support the ones of us that are right, and I need for you to stand (up) to those that are not right."
The federal Justice Department is leading the investigation into Mr Sterling's death.
Data from The Washington Post shows already this year, police have shot and killed 123 black Americans.
The total number of fatal police shootings for 2016 is 506.
