Video report by ITV News Reporter Mark McQuillan
A woman has been killed and three others, including an eight-year-old girl, have been injured after a gunman opened fire in a US synagogue as worshippers celebrated Passover.
Shortly after fleeing the scene in Poway, a city 17 miles north of San Diego, the gunman called police and was arrested.
The suspect has been named as 19-year-old John Earnest.
San Diego County Sheriff William Gore said Earnest has no criminal record, but investigators were looking into a claim he made in an online manifesto about setting a fire at a mosque in nearby Escondido last month, Mr Gore said.
Mr Gore added that authorities were reviewing copies of his social media posts and were investigating the attack as a possible hate crime.
The attack comes exactly six months since 11 people were killed in a shooting at a Pittsburgh synagogue in the deadliest assault on Jews in US history.
US President Donald Trump took to Twitter to offer his "thoughts and prayers to all of those affected by the shooting".
When a Rabbi came face to face with the gunman
Lori Kaye, 60, of Poway was killed, Rabbi Yonah Fradkin, executive director of Chabad of San Diego County, said in a statement.
Rabbi Yisroel Goldstein, whose right index finger was blown off in the gunfire, recalled the moment he came "face to face" with the gunman to NBC's Today programme.
"I heard a large bang or noise, I thought maybe a table fell," he said.
"I was face to face with this murderer who was holding a rifle and looking straight at me and as soon as he saw me he started to shoot towards me, and that's when I put my hands up and my fingers got blown away.
"And then he continued on and just killed Lori Kaye right there on the spot. I turned around and saw a group of children, I just ran not even knowing my fingers were blown off and just hurled all the kids together and got them outside."
He descrbed shooting victim Lori Kaye as a "kind-soul" who everyone in the community knew. She was a founding member of the congregation along with Rabbi Goldstein.
The community "will not be intimidated or deterred" and the "terrorists will not win", he vowed.
Sheriff Gore said the gunman used an AR-type assault weapon, and there were indications that the weapon might have malfunctioned after firing numerous rounds inside the synagogue.
An off-duty Border Patrol agent working as a security guard at the Chabad of Poway fired at the shooter as he fled, missing him but striking his getaway vehicle, he added.
Shortly after fleeing the scene, Earnest called police to report the shooting, San Diego Police Chief David Nisleit said.
When an officer reached the man, “the suspect pulled over, jumped out of his car with his hands up and was immediately taken into custody,” Mr Nisleit said.
As well as Rabbi Yisroel Goldstein, eight-year-old Noya Dahan, and Almog Peretz, 34, were also injured.
All of the injured are said to be in stable conditions.
Those in the synagogue had been celebrating Passover, a week-long commemoration of the deliverance of the ancient Hebrews from slavery in Egypt.
“In the face of senseless hate we commit to live proudly as Jews in this glorious country,” Rabbi Yonah Fradkin said in his statement.
“We strongly believe that love is exponentially more powerful than hate.
"We are deeply shaken by the loss of a true woman of valour, Lori Kaye, who lost her life solely for living as a Jew.”
There was no known threat after Earnest was arrested, but authorities boosted patrols at places of worship as a precaution, police said.
Minoo Anvari, a member of the synagogue, told local media that her husband was inside during the shooting.
She said he called to tell her the shooter was shouting and swearing.
She called the shooting “unbelievable” in a peaceful and tight-knit community.
“We are strong; you can’t break us,” Ms Anvari added.
Donny Phonea, who lives across the street from the synagogue said he heardsomeone shout, “Police!” Then he heard three or four shots.
The 38-year-old bank auditor looked over his fence facing the synagogue and saw people hiding behind an electrical box in the car park of a neighbouring church.
At that point, he knew something was “very, very wrong”, went inside and closed his doors.
“I’m a little taken aback,” said Mr Phonea, who moved to Poway two weeks ago.
“I moved here because safety was a factor. Poway is very safe.”
As well as tweeting about the attack, Mr Trump offered his sympathies on Saturday, saying the shooting “looked like a hate crime” and calling it “hard to believe”.
“Our entire nation mourns the loss of life, prays for the wounded and stands in solidary with the Jewish community,” Mr Trump said later at a rally in Wisconsin.
“We forcefully condemn the evils of anti-Semitism and hate, which must be defeated.”
The mayor of Poway, who tweeted that he got a call from the President offering help, also denounced what he called a hate crime.
“I want you know this is not Poway,” Mayor Steve Vaus said.
“We always walk with our arms around each other and we will walk through this tragedy with our arms around each other.”
Democratic Governor Gavin Newsom said he joins the community in grief.
“No one should have to fear going to their place of worship, and no one should be targeted for practising the tenets of their faith,” he said.
Residents of Pittsburgh gathered at the Tree of Life synagogue for a vigil in the wake of the Poway shooting.
Pittsburgh mayor Bill Peduto tweeted a picture of the gathering of over 100 people in a steady rain.
It was accompanied by text that read: “We gather. Again. Always. Until we drive hate speech & acts of hate out of our city, our state, our nation, our world."
The Tree of Life released a statement, saying “We know first-hand the fear, anguish and healing process such an atrocity causes, and our hearts are with the afflicted San Diego families and their congregation.”