A neighbour described the aftermath of a shooting at a bar in California as “like a battlefield” as wounded victims fled from a hooded killer armed with smokebombs and a handgun.

Police in Thousand Oaks said 12 people were shot dead when Ian David Long, a 28-year-old former US Marine with mental health problems, opened fire inside Borderline Bar and Grill on Wednesday night.

Terrified drinkers used bar stools to smash windows as they desperately tried to escape the gunfire at the venue popular with students from nearby California Lutheran University.

A sheriff’s sergeant is among the dead and Long is believed to have killed himself.

Sarah Silikula lives minutes away from the bar and first realised something was wrong when she heard screaming.

She told the Press Association: “A few minutes earlier I noticed the music had stopped but really didn’t process that it was a big deal until I heard slight screaming. It’s very unusual to hear anything in this neighbourhood after sunset, it’s a quiet place.

“So I was about to walk outside when my daughter called and said, ‘don’t go outside, lock your house up, there’s an active shooter at Borderline. They don’t know where he is’.”

“I said ‘how do you know where this is at, there’s nothing on the news?’ She said ‘I was supposed to go to Borderline tonight but I didn’t go, I stayed home. My friends are there, and I just talked to one of them she’s hiding in the bathroom’.”

Mrs Silikula, a mother of eight, then left her house and saw dozens of police cars descending on the bar.

The 44-year-old praised their bravery and said officers “did not hesitate” before rushing inside.

California Bar Shooting
Mourners embrace outside the Thousand Oaks Teen Centre (Marcio Jose Sanchez/AP)

The injured then started to leave Borderline, desperately staggering to safety.

Mrs Silikula said: “The kids were running this way, like a tsunami of injured children. It was like a battlefield, you know when you carry soldiers off a battlefield?

“They were carrying their friends, they had no clothes on and they were missing their shoes and had covered up gunshot wounds with their shirts. You just don’t know what to do but comfort them and pull them around.”

Mrs Silikula spoke to one victim who told her they had been hiding in the bathroom as the sound of gunshots got closer.

The door opened as they were cowering in a stall and the barrel of a gun poked through before the police officer holding the weapon entered and guided the young girl to safety.

California Bar Shooting
Sheriff’s Sgt Ron Helus was killed after a gunman opened fire in California (Ventura County Sheriff’s Department via AP)

Sheriff’s Sergeant Ron Helus arrived at Bordeline around 11.20pm local time and entered the building after hearing gunshots, US police said.

He was immediately hit with bullets and later died. Ventura County Sheriff Geoff Dean said: “He went in there to save people and paid the ultimate price.”

Mrs Silikula said the neighbourhood was in shock. She added: “It’s so hard to believe. No-one locks their doors here, people forget to lock their cars all the time. It’s just not where anyone expects this is going to happen.”

Authorities say it is the deadliest mass shooting in the US since 17 teachers and students were gunned down at a Parkland, Florida, high school nine months ago.

And it comes less than two weeks after a gunman killed 11 people at a synagogue in Pittsburgh.

Mrs Silikula begged Donald Trump to tighten gun laws to prevent further tragedies.

She said: “A week ago I would say it’s your business. Everyone has a right to get a gun. But not anymore, now I beg our president to stand up for our children, I challenge him to do it.

“He stands up to so many other people, he screams and yells to get his point across. I want him to scream and yell for our kids’ safety so my little kids don’t have to worry about this happening to them when they go to school or when they go out.

“This should never happen again.”

Mr Trump praised police for their “great bravery” in the California attack and said, “God bless all of the victims and families of the victims”.