Six years after a deadly mass shooting occurred in Seal Beach, California, in which nine people were killed, another shooting incident Sunday night kept the Seal Beach police and SWAT team members on alert as they responded to a "tactical situation" after gunshots were heard in the area. There is a possibility of an armed man, reportedly an off-duty cop, barricading himself inside an apartment complex in the area of 7th Street and Central Avenue, reports said.

The situation has compelled police officers to urge the residents to stay indoors, reports said.

A woman dialed 911 at about 7:20 p.m. local time (10:20 p.m. EDT) asking for help, Seal Beach police Sgt. Michael Henderson said. The police said the line went dead immediately after the woman's call. 

Multiple witnesses said they heard gunshots fired in the apartment building, according to a report.

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A barricade situation continued till late night. "This is an ongoing tactical situation," said Henderson adding, "The SWAT team has been deployed."

Officers tackled the situation with precaution and expanded the lockdown area after 10 p.m. local time.

Dylan Bolander, a 14-year-old who lived on the second floor of a building along 7th Street near Central Avenue, told police about the moment he heard the gunshots. According to Bolander, a woman staying on the top floor came down running asking for help. She looked petrified and told Bolander that a man staying next to her apartment was an off-duty cop whom she had overheard yelling at his girlfriend. Moments before the gunshots were fired, the woman overheard the cop's girlfriend yelling, "No, don’t do this," Bolander told the police.

It is not known whether the shooter's girlfriend is alive or not, reports said.

Another witness, Greg Meier, who works as a maintenance man in the building and lives on the first floor, said he returned home after having dinner at a nearby restaurant and was watching TV when he heard three gunshots, the Orange County Register reported. He added: “Next thing I know police are showing, barricading the street and running around with guns."

Several people residing in the area took to Twitter asking about the current situation while those who are not aware of what had happened, expressed concern.

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Henderson said the SWAT team is using "technology to ensure the safety of officers" while determining whether the suspect and/or victim were inside the apartment. No further gunshots were reported, he said, according to NBC Los Angeles.

In 2011, a gunman burst into a beauty salon in Seal Beach and went on a shooting rampage killing nine people. The attacker was reportedly loaded with weapons when he attacked the salon. After shooting down people, he stormed out of the salon, jumped into a car and fled, according to the New York Times.