A live video feed showed the gas station cordoned off by yellow tape and guarded by police, some in helmets and carrying riot shields, with bystanders shouting at them in a tense standoff.
The Internet is ablaze in protest over the incident:
If you know #AntonioMartin please tweet positive things, pictures, etc about him. Let's stop the 'thug' narrative. He was a man.— Vivrant Thang (@_MissBre) December 24, 2014
Sad How The Same Outcome Keeps Occurring Yet There Still Is No Change . #AntonioMartin— D???e? ???quez (@danielmarquezzz) December 24, 2014
Each time I feel like I lost a family member. So hurt and disgusted to call this place my country. #AntonioMartin— Makya (@itsKya_tweeties) December 24, 2014
Right now they are probably going through #AntonioMartin Facebook and Instagram to find the best pictures to criminalize and demonize him!!— Robbie?Jones (@robbieisreal) December 24, 2014
The St. Louis Post-Dispatch newspaper reported that some 60 people had gathered at the scene and that at least three people were arrested. Images and video footage showed what appeared to be smoke and loud bangs, although it was not clear whether it was the bystanders or the police that had caused them.
Police said the man had pointed a handgun at an officer who approached him and another man outside a gas station where the officer was "conducting a routine business check" in the suburb of Berkeley.
"Fearing for his life, the Berkeley Officer fired several shots, striking the subject, fatally wounding him," St. Louis County Police Department spokesman Brian Schellman said in a statement. The second man fled the scene.
The St. Louis Post-Dispatch named the dead man as 18-year-old Antonio Martin, citing his mother. The police said they could not confirm his identity.
Berkeley neighbors the suburb of Ferguson, where police officer Darren Wilson shot Michael Brown on Aug. 9, a killing that fueled criticism of the way police and the criminal justice system treat minority groups.
Protests in Ferguson have taken place for months and spilled over into violence when a grand jury decided not to charge Wilson.
Demonstrations in cities across the country gained in momentum when a New York grand jury decided not to charge police over the death of Eric Garner, a 43-year-old black man who police tackled and put in a chokehold.
The shooting victim’s mother, hysterical at the news of his death, has been filmed crying out "That's my baby!"
Meanwhile, about 200 people marched in New York on Tuesday, defying Mayor Bill de Blasio's call for protests to be suspended after two police officers were killed in their patrol car on Saturday in an apparent revenge attack.
In Los Angeles, police said they would investigate whether any officers were involved in singing a song that poked fun at the Ferguson killing at a party organized by a retired policeman.
The lyrics of the song, on a video posted on entertainment news website TMZ, said: "Michael Brown learned a lesson about a messin' with a badass policeman."