(CNN) Four people, including a police officer and three people believed to be civilians, were killed during an hours-long standoff and firefight Tuesday between two suspects and law enforcement in Jersey City, New Jersey, authorities said.

Two suspects were also killed, Jersey City Police Chief Michael Kelly told reporters.

The fallen officer was identified as Det. Joseph Seals, a 15-year veteran of the department, Kelly said.

Seals was part of a statewide anti-violence unit, and Kelly credited him with removing "dozens and dozens" of handguns from the street.

"We believe he was killed while trying to interdict these bad guys," Kelly told reporters, adding, "Once again, this is all being investigated."

The officer who was killed is believed to have been ambushed, according to a law enforcement source.

Two officers and one civilian were in stable condition after being struck by gunfire, Hudson County Prosecutor Esther Suarez said via Twitter. The wounded officers were identified by Kelly as Ray Sanchez and Mariela Fernandez. They were both treated and released.

Hours after the first gunshots, the details of what led to the incident and how it unfolded remain unclear.

Police officers arrive at the active shooting scene in Jersey City on Tuesday.

The gunplay went on for hours

The shooting began at about 12:30 p.m. ET and drew reinforcements from neighboring jurisdictions, police said, virtually shutting down commerce in some areas and forcing schools to go on lockdown.

CNN affiliates reported the shooting occurred in the area of Martin Luther King Drive in Jersey City, across the Hudson River from Manhattan.

The chaotic scene unfolded on city streets, where bursts of gunfire and blaring sirens were heard as heavily armed officers moved in, according to footage shared on social media.

Continuous gunshots could be heard in Jersey City for at least 20 seconds prior to 2 p.m., according to a CNN producer at the scene. At least three armored personnel vehicles were on scene, the producer said. Paramedics responded as helicopters hovered overhead.

The gunplay continued for hours before authorities announced the suspects had been killed during a standoff with police in another part of town.

A source said earlier that at least one shooter was "neutralized" inside a bodega. Law enforcement sent in a robot to have eyes and ears inside the store where the shots were fired, the source said.

The investigation

The investigation will take weeks and could stretch on for months, Kelly said. "The crime scene is very extensive," he told reporters, "and is at three locations, at least."

Part of the investigation involves a stolen U-Haul truck, which Kelly said may contain an incendiary device and was being examined by the bomb squad.

There is no indication of terrorism, Jersey City Department of Public Safety Director James Shea said.

The ATF office in Newark tweeted Tuesday that agents responded to "reports of an active shooter."

Police officers arrive at the scene following reports of gunfire Tuesday in Jersey City.

The New York Police Department's Emergency Service Unit also responded, according to a law enforcement official familiar with the incident.

No one was in custody in connection with the shooting, according to a law enforcement official.

In a brief news conference Tuesday evening, New Jersey Gov. Phil Murphy praised the efforts of law enforcement, who "responded to this incident not knowing what they were entering, or if they would even make it out."

"If not for them," Murphy said, "I shudder, we shudder to think about how much worse today could have been."

The New Jersey State Police Benevolent Association tweeted: "We need a lot of prayers right now for Jersey City officers. Keep all those involved in your thoughts."