Six people, including a New Jersey police officer, were killed in an hourslong standoff and shootout that brought a Jersey City neighborhood to a standstill Tuesday, investigators said.

The shooting unfolded at a Jewish market near the Sacred Heart School. The shooters had "targeted" the market in their attack, Mayor Steven Fulop said late Tuesday.

Of the six people who died, one was Detective Joseph Seals, 40, who was married with five kids. The others killed included the two shooters and three civilians.

A second officer was struck in the shoulder by gunfire, and two others were hit by shrapnel, Fulop added.

"Based on our initial investigation (which is ongoing) we now believe the active shooters targeted the location they attacked. Due to an excess of caution the community may see additional police resources in the days/weeks ahead. We have no indication there are any further threats," he tweeted.

The situation forced every public school in Jersey City into lockdown mode for hours. The FBI was assisting Jersey City police.

"Our thoughts and prayers are with the men and women of the Jersey City Police Department, especially with the officers shot during this standoff, and with the residents and schoolchildren currently under lockdown," Gov. Phil Murphy said in a statement. "I have every confidence in our law enforcement professionals to ensure the safety of the community and resolve this situation."

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Loud volleys of gunfire could be heard at regular intervals but subsided around 2 p.m. in the city, which is just across the Hudson River from Manhattan.

Dozens of bystanders pressed against the police barrier to film the action on cellphones, some whooping when gunfire bursts filled the air.

Andy Patel, who works at a liquor store about three blocks away from the site of the shooting site, said there had been consistent gunfire for about an hour Tuesday afternoon.

"I can hear the gunshots. It's like firecrackers going off. They were shooting like crazy about an hour ago. Then it stopped for like 20 or 30 minutes. The cops were clearing everyone off the streets," said Patel.

President Trump tweeted: "Just received a briefing on the horrific shootout that took place in Jersey City, NJ. Our thoughts & prayers are w/ the victims & their families during this very difficult & tragic time. We will continue to monitor the situation as we assist local & state officials on the ground."

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The Bureau of Alcohol, Tobacco, Firearms and Explosives said it was responding. The New York Police Department sent emergency services personnel, and the force's counterterrorism unit was monitoring the situation.

Several schools in the area were placed on lockdown while the situation is ongoing, officials said. Jersey City Public Schools tweeted "all students and staff are safe."

The Associated Press contributed to this report.