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JERSEY CITY, N.J. (AP) — Six people, including a police officer and three bystanders, were killed in a furious gun battle Tuesday that filled the streets of Jersey City with the sound of heavy fire for hours, authorities said.

The dead included the two gunmen, Jersey City Police Chief Michael Kelly said.

The slain officer, Detective Joseph Seals, 40, was credited by his superiors with having led the department in the number of illegal guns removed from the streets in recent years, and might have been trying to stop an incident involving such weapons when he was cut down by gunfire that erupted near a cemetery, authorities said.

The shooting then continued at a kosher supermarket about a mile away, where five more bodies were found, Kelly said.

“It’s a really tough day for the city of Jersey City,” Mayor Steven Fulop said. Seals “was one of the best officers for getting the most guns off the streets. He was a good cop.”

Two other officers were wounded but were later released from the hospital, authorities said.

The bullets started flying early in the afternoon in the city of about 270,000 people, situated across the Hudson River from New York City. Seals, who worked for a unit called Cease Fire, was shot around 12:30 p.m. The gunmen then traveled to another part of the city in a stolen rental van and engaged police in a protracted shootout.

“Our officers were under fire for hours,” the chief said.

Inside the grocery store, police found the bodies of what they were believed were the two gunmen and three other people who apparently happened to be in the place when the assailants rushed in, authorities said. Police said they were confident that all those killed were shot by the gunmen and not by police.

The kosher grocery is a central fixture in a growing community of Orthodox Jews who have been moving to Jersey City in recent years. Authorities were unable to say why the gunmen went there.

City Public Safety Director James Shea said that authorities believe the bloodshed was not an act of terrorism but that it was still under investigation.

The shooting spread fear through the neighborhood, and the nearby Sacred Heart School was put on lockdown as a precaution.

SWAT teams, state police and federal agents converged on the scene, and police blocked off the area, which in addition to the school and supermarket included a hair salon and other shops. Dozens of bystanders pressed against the police barrier to capture the action on their cellphones, some whooping when bursts of fire could be heard.

Video shot by residents recorded loud volleys of gunfire reverberating along one of the city’s main streets and showed a long line of law enforcement officers pointing guns as they advanced, yelling to bystanders, “Clear the street! Get out of the way!”

“ It’s like firecrackers going off,” said Andy Patel, who works at a liquor store about three blocks away. “They were shooting like crazy. … The cops were clearing everyone off the streets.”

Seals had been on the Jersey City Police Department since 2006. In addition to his work with the illegal guns unit, he was cited for heroism in a Christmas Eve 2008 incident in which he and another officer burst through the window of a home and stopped a sexual assault that was being carried out against a 41-year-old woman.

Seventh grader Zamir Butler said his class was coming back inside from the playground at Sacred Heart, which sits across the street from the grocery store, when he heard the shots. At first he thought they were thunder, since it had rained earlier. “Everybody was running up the stairs to get to safety in the classroom,” he said. “A few of the kids were crying. They told us to stay behind the wall and stay down.”