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 drove a stolen rental van to another part of the city and engaged police in a lengthy shootout.

Kelly said when police responded to the area of the kosher store, officers “were immediately engaged by high-power rifle fire.”

A video shot by a witness shows a police officer on the ground by a car, apparently wounded. Another officer goes to him, helps him up and the two run around a corner as gunshots ring out. Seconds later, as a police cruiser pulls up in front of the store, about a dozen shots are heard in rapid succession.

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