A marathon standoff following a shootout between deputies and a barricaded suspect in a Los Angeles County residence has been ongoing for over 18 hours, authorities said.

Los Angeles County Sheriff's deputies responded to a home in Valinda around 2:30 p.m. local time on Friday, following a report of an "assault with a deadly weapon," the sheriff's department said in an advisory.

"When they arrived, they were met with gunfire by the suspect and deputies returned fire at that time," Deputy Miguel Meza told reporters. "The suspect barricaded himself inside that residence. We don't know if that residence is his or family members."

Crisis negotiations are on the scene and are "attempting to contact the suspect to resolve this situation peacefully," the sheriff's department said.

Some of the male suspect's family members were assisting police by providing information on "what state of mind he was in," Meza said.

The standoff was still underway as of 11:30 a.m. local time Saturday, a spokesperson for the sheriff's department confirmed.

No one has been hit by gunfire, the department said. A female victim was transported to a local hospital for an undisclosed injury that was not a gunshot wound, deputies said.

The surrounding homes have been evacuated and residents are advised to avoid the area. Amorored equipment including BearCats and battering ram vehicles could be seen on the scene. Paramedics were also on standby.

Eric Torres told ABC Los Angeles station KABC Friday night that he was unable to get home due to the ongoing incident.

"I heard gunshots, and then more gunshots," he told the station. "I think I might have heard 20 or 30."