An Adelaide man has been arrested after posting a disturbing photo on social media, which appeared to threaten violence towards a local mosque.

“On the way to my local mosque to introduce these f**** to my Lord and Saviour Jesus Christ. Amen,” he wrote, accompanied by a photo of him holding what appears to be a large automatic rifle.

In the wake of the Christchurch massacre, South Australian police were not taking any chances and within two hours, they had swooped on the suspect’s home.

7NEWS cameras were there as officers raided his western suburbs home late on Sunday night, marching him into a police car.

Man claims 'joke'

The man has told 7NEWS the post, which was shared in a private Facebook group, was simply a "joke", and says the gun is a plastic toy.

He was detained under the Mental Health Act, but has been released from hospital while investigations continue.

It comes just weeks after another Adelaide man faced court over a social media tirade appearing to praise the Christchurch massacre.

Chad Vinzelberg was arrested following a tip-off from 7NEWS, after he posted comments allegedly supporting the attack in New Zealand that killed 50 people and left dozens more injured.

"So happy to see this happen," Vinzelberg wrote on Facebook.

"Thank you for the video bud, absolute champion."

SA Police warns that comments made online can have real-world consequences and anything concerning or suspicious should be reported to the National Security Hotline on 1800 1234 00, or in an emergency, to triple 0.