Graffiti left after an alleged arson attack at a California mosque referenced the Christchurch terror attack in which 50 Muslim people were gunned down on March 15.

A fire broke out around 3am Sunday at the Islamic Center of Escondido, located roughly 50km north of San Diego, NBC reported.

People inside the mosque were able to put the fire out before firefighters arrived. There was visible scorching to one side of the mosque, NBC reported.

Police said the suspect left a note in the mosque's parking lot referencing the New Zealand attacks.

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The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives are investigating the incident along with local police, but no arrests have been made so far.

The San Diego office of the Council on American-Islamic Relations condemned the apparent arson attack and encouraged anyone with information to come forward.

"A little more than a week after 50 Muslim worshippers in New Zealand were brutally massacred at the hands of a white supremacist terrorist who cited Donald Trump in his hate manifesto, that same hatred has resurfaced in Escondido," CAIR-SD Executive Director Dustin Craun said in a statement.

He continued: "It is disturbing enough that some sick individual would attempt to burn a house of worship to the ground, but referencing the slayings in New Zealand is beyond the pale. While the majority of humanity has responded to the tragedy to draw closer to one another and refute hatred, a violent and hate-filled minority seeks further divisions."