A gunman has opened fire at a synagogue in California, leaving one woman dead and three other people injured, police say.

A 19-year-old man has been arrested after the attack at Poway, north of the city of San Diego.

The synagogue had been hosting a Passover celebration when the gunman burst in, reports said.

Police have not suggested a motive but US President Donald Trump said the attack appeared to be “a hate crime”.

The shooting comes six months after a gun attack killed 11 people at the Tree of Life synagogue in Pittsburgh. It was the worst anti-Semitic attack in recent US history.

San Diego County Sheriff Bill Gore told reporters that investigators were reviewing the suspect’s social media activity and examining an open letter published online.

Authorities later named him as John Earnest, the Associated Press reported, and said he was also under investigation in connection with a fire at a mosque last month.