It is Sunday morning at Hillsong's megachurch in the Sydney suburb of Alexandria, and Pastor Natalie Pingel pauses mid-sermon to conduct an impromptu Dwayne "The Rock" Johnson look-a-like contest.

Key points: Pentecostal churches are growing, while other Christian denominations are declining

Pentecostal churches are growing, while other Christian denominations are declining The denomination began in Los Angeles in the early 1900s before arriving in Australia

The denomination began in Los Angeles in the early 1900s before arriving in Australia Modern Pentecostals in Australia often embrace 'prosperity doctrine'

She selects a group of buff parishioners and members of the band to line up on stage. Each takes turns flashing the crowd the actor's signature raised eyebrow, to approval and gushing laughter.

Pastor Pingel then leads the congregation in prayer, the band plays anthemic rock music and the big screens either side of the stage light up with suggestions for what people can pray for.

The suggestions include financial stability, luck with job applications and visa approvals.

A rock-concert sensibility isn't the only thing setting Pentecostal churches apart. ( ABC: Tim Leslie )

Pentecostalism is not just about rock music and laughs, it also promises the Holy Spirit can help you in this life, in practical ways, not just in the afterlife.

This "prosperity doctrine" is key to how Pentecostal Christianity is attracting new demographics of worshippers, particularly migrants and young people.

How popular is Pentecostal Christianity?

The Pentecostal church has succeeded where other Christian denominations are struggling.

"Australia's largest churches in every capital city and in the regions are all Pentecostal churches," said Andrew Singleton, an Associate Professor of Sociology and Social Research at Deakin University.

"Starting with Hillsong in Sydney and churches in Melbourne and Adelaide like Planet Shakers, Riverside Church, Paradise Church are all Pentecostal.

"More people are attending Pentecostal churches than any other Christian denomination, they put bums on seats."

The last census showed a marginal increase in the number of Australian Pentecostals, from 220,000 in 2006 to 260,500 in 2016, while other religions declined.

It is also polling well with young people, with people under 30 making up a large section of the congregations.

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"If I'm a 22-year-old and I'm religious, do I look at the local Catholic Church?" Associate Professor Singleton said.

"I see a bunch of old ladies.

"Do I look at that or do I look at the Pentecostal church down the road where I see hundreds of people my own age, dressed like me?

"It's a no-brainer."

Michael, a 25-year-old parishioner at Hillsong's Sunday service, agreed.

"Right now everyone is very into experience and Pentecostalism was birthed out of experience of the Holy Spirit," he said.

"It's exciting, it's riveting, there's a little bit more life and energy in it," his friend Maddy added.

How did it become popular in Australia?

Pentecostalism grew from small churches like the Azusa Street Revival in Los Angeles in the early 1900s.

The first meetings featured mixed-race congregations, free-form sermons without a strict running order and parishioners experienced miracles such as healings.

According to Associate Professor Andrew Singleton, pockets of the movement sprung up in Australia in the 1920s.

An independent Pentecostal group gathers in Brisbane in the 1930s in front of the tent in which they would congregate. ( Supplied: Brisbane City Church )

"It was a marginal church movement that didn't have many people all the way through until the 1960s," Associate Professor Singleton said.

"A really ramshackle affair."

The breakthrough came when Pentecostals began borrowing from a group called the Jesus People in the 1960s, taking on an informal style and using music to evangelise.

"It's really had this epic journey from the margins to the mainstream," Associate Professor Singleton said.

"From the 1970s for the next couple of decades they really started to grow in what we call the 'bible belt,' which is the outer suburbs of Brisbane, Sydney and Melbourne.

"They would form these congregations, they weren't weighed down by any need to get approval from the Catholic or Anglican hierarchy, literally anyone who could get some musicians together and some dynamic preaching, set up in a school hall, and away they go."

Associate Professor Singleton said the Pentecostal's exceptional ability to gather donations allowed them to expand.

"They would have enough money to establish congregations, buy their own buildings and then you'd see something like Hillsong, which began as The Hills Christian Life Centre in Baulkham Hills in Sydney able to purchase land and build that epic stadium," he said.

The evolution of the church over recent decades meant it has undergone a rebirth of sorts.

"A lot of the baby boomers who founded it have moved on, left church, because it's high energy, it's hard to stay committed to that practice," Associated Professor Singleton said.

"Increasingly migrants from overseas, if they're coming from majority Christian countries or sub-Saharan Africa or Oceania or Latin America they're actually Pentecostals and they're forming their own congregations.

"For example, where I live [in Melbourne], we've got several African Pentecostal churches.

"So there's this new kind of shape to the Pentecostal experience in Australia."

What is the difference between Pentecostals and other Christians?

One of the most recognisable aspects of a Pentecostal church is the singing and music and Hillsong has made music central to its model.

"They really used music as their engine, they wrote their own music and it's now famous worldwide," Associate Professor Singleton said.

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While the music and singing is front and centre, some worshippers also speak in tongues, an incomprehensible language.

They also practice something called "slain in the spirit", where worshippers fall to the ground in a state of religious fervour.

"It's kind of what makes Pentecostals distinctive," he said.

"They believe the Holy Spirit is really active in a person's life and spiritually energises them in an everyday way."

Do not expect to see those elements on your first trip to one of these churches though.

"The version of Pentecostalism that reigns supreme in Australia now is a very soft kind of version compared to earlier iterations where it was much more religiously edgy," he said.

He said the more "gonzo" spiritual experiences are becoming less important today.

Instead, modern Pentecostalism focuses on teaching God will help you be successful. This is what has been dubbed the "prosperity doctrine".

"God doesn't necessarily want you to be richer, but God wants you to be successful and a manifestation of that might be getting your finances in order," he said.

According to Associate Professor Singleton, from a political point of view, they sit to the right.

"They're very socially conservative when it comes to issues of marriage equality, LGBTQI rights, religious education at schools, religious freedoms," he said.

Will Pentecostalism become more influential?

Prime Minister Scott Morrison is a dedicated Pentecostal worshipper, promising Australians in the lead-up to the federal election, "I'll burn for you", a phrase used in the church to signify a dedication to service.

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He was pictured just before the election at a service at Horizon Church in Sydney's south and when he won the poll, he told cheering Liberal supporters: "I've always believed in miracles."

It is not unusual for a politician to have religious affiliations, because religious people tend to be motivated to get involved in politics, and Associate Professor Singleton said it was only a matter of time before a Pentecostal reached high office.

"We've had a long line of religious prime ministers but he's the first Pentecostal and probably not the last," he said.

Prime Minister Scott Morrison and his family attend Horizon Church, a Pentecostal church based in the Sutherland Shire of Sydney. ( AAP: Mick Tsikas )

While we can expect another prime minister cut from the same cloth as Mr Morrison, according to Associate Professor Singleton, do not expect the church's political influence to grow.

"I personally think that we've probably plateaued in terms of influence of Pentecostalism and other religious organisations in Australia," he said.

"The tide of secularism is strong and powerful.

"All the research shows teenagers falling away from organised religion one generation after the next and Pentecostalism has kind of bucked that trend, but how long can you resist? I don't think forever."