Six people including a police officer and two suspects were killed during an hours-long shoot-out on Tuesday across Jersey City, a New York suburb not far from the Statue of Liberty.
"Our officers were under fire for hours," Jersey City Police Chief Michael Kelly told reporters after the latest high-profile US shooting.
In addition to the death of an officer and the suspects, three civilians were also died in the incident that began around midday at a cemetery and ended in a store on Dr Martin Luther King Drive in lower Jersey City. Five of the dead were found inside a store, said Chief Kelly.
"We believe that two of them are bad guys," while the other three are civilians, he said, describing the crime scene as "very extensive, three locations at least".
Two other officers were wounded. Chief Kelly said the suspects' "movement was rapid and continuous for four hours" during the drama which resulted in the deployment of hundreds of police from New Jersey and New York, including tactical officers armed with rifles and dressed in olive-green fatigues.
NBC television reported that hundreds of rounds were fired, and media reports said the shooting began when an officer investigating a homicide approached the suspects in the cemetery.
He was the first victim, identified by media as Detective Joseph Seals.
Asked to confirm whether the officer was indeed probing a murder, Mr Kelly said it is "being looked into".
The suspects then took refuge in a grocery store where the shooting continued and the five bodies were later found.
US shootings have become a social normality for residents throughout the United States in venues including churches, schools, and cinemas. Firearms were linked to nearly 40,000 deaths of various kinds in 2017, according to the Centres for Disease Control and Prevention.