Cases of demonic possession are not only increasing in number, "as the years go by, the cases are getting darker," an exorcist has warned. 

James Cloud, of the Advent Catholic Church in Oregon, told KOIN 6 news network that interest in oujia boards and drug-taking could be behind an increase in demand for exorcisms.

While the Gospels record numerous instances of Jesus casting out demons, Cloud said that too many churches have a "very sanitized" view of the spiritual world. 

He admitted, though, that he would have found it hard to believe some of the things he had encountered if he were not an exorcist. 

"If I hadn't seen half the stuff I've seen in life, I wouldn't believe it, either — until it actually happens," said Cloud.

"Throughout the scriptures, we see examples of angels interacting on Earth — devils and Satan himself interacting on Earth."

Cloud, who is also a licensed counsellor, said that with each case, he weighs up whether the symptoms suggest a mental health issue or whether they point to a problem rooted in demonic possession. 

"Many things that would almost mirror someone that's being possessed or oppressed — many mental health conditions will do it too," he said. 

"I have to differentiate: is this substance use, is it mental health, or is it a legitimate issue that's going on? ... So, if I can rule out the first two then what I'm left with is something that's potentially legitimate."

Italian Professor Giuseppe Ferrari, founder and secretary of the Social and Religious Research and Information Group, told a gathering of exorcists in Rome earlier this year that the demand for exorcisms was linked to dabbling in the occult, and that young people were particularly at risk. 

"Many young people display a certain attraction and interest toward themes tied to esotericism, magic, the occult, Satanism, witchcraft, vampirism and contact with a presumed supernatural world," he said.

"Some end up accepting as spiritual leaders these characters who, while proposing a flawed liberty and false freedom, only aim at taking hold of their existence." 

Dr Richard Gallagher, a psychiatry professor from New York who was invited to conduct a discernment process by a group of exorcists, told the Daily Mail last year that he also blamed the occult for many cases of demonic possession.

"It's not random at all; there's almost always a discernible cause," he said.

"The most common cause ... is someone has turned to evil or the occult. And paradoxically, it's often when they try to get away from that that the demonic world feels they have a hold on that person."