A former member of South Korea's Grace Road Church says she has given evidence to South Korean police in the hope the group's founder will be prosecuted and jailed.

Key points: Grace Road leader Shin Ok-ju was arrested for detaining 400 followers and administering beatings

Grace Road leader Shin Ok-ju was arrested for detaining 400 followers and administering beatings It is alleged that a 70-year-old man died following a physical assault

It is alleged that a 70-year-old man died following a physical assault Seo-Yeon Lee says the group has ambitions to be highly influential in Fiji

Seo-Yeon Lee fled the church's Fiji compound in 2014, leaving behind her mother and 11 other members of her extended family.

The controversial church leader, Shin Ok-ju, was arrested in South Korea in early August where she is being investigated for detaining about 400 of her followers in Fiji as well as for physically assaulting some of them.

Ms Lee said she never believed the pastor's teaching, but was drawn into the group by her mother.

"I was pretty much coerced into getting involved," Ms Lee told the ABC's Pacific Beat program.

"I was going to school in the US and my mother was diagnosed with uterine cancer.

"The church did not want her to get treatment. They believed that doctors were implanting chips into her while she was unconscious."

Ms Lee said she agreed to follow her family to Fiji on the condition her mother first seek to medical treatment.

"My mother lied to me and said she wanted to move to Fiji to recover and she said, 'stay with me for two weeks then you can return to Korea'.

"When I actually arrived in Fiji and realised she was moving to a compound owned by the church, that's when I knew I was in big trouble."

Many of Ms Shin's followers travelled to Fiji in 2014 because they reportedly believed that Fiji had been chosen by God to prepare the world for a major famine and drought.

'My passport was gone … I freaked out'

Ms Lee raised $7,000 to support herself after fleeing Fiji. ( GoFundMe: Cecilia Lee )

Ms Lee said she had given her passport to her mother for safe keeping.

"I asked my mum for my passport and she said it was gone, so that's when I freaked out," she said.

"I called the police and asked them to come and pick me up and take me to the police station but when I had my back turned somebody called the police station back, saying it was a prank call or the girl who called was insane, then they ripped the landline out of the wall.

"I ran out of the compound and luckily the police were making rounds … they took me to a police station and that's where they connected me to the Korean embassy and they issued an emergency passport."

Mainstream churches in Fiji have long accused Grace Road of being a cult.

"I think it is common knowledge here that the movement is a cult movement from our observation and the stories that we hear from members of the church," Wilfred Regunamada, a spokesman for the Methodist Church, told Pacific Beat recently.

Ms Lee is not the only ex-church member to flee.

South Korean TV aired a documentary late last month featuring the testimony of a number of former church members detailing physical abuse and overwork, as well as showing footage of church leader Ms Shin hitting and abusing her followers.

John Power is a journalist who spent six years working in South Korea.

"Shin Ok-ju claims to have the authoritative interpretation of the bible and she says she alone is able to read it as it's intended, and she claims Fiji is named in the bible as a paradise where a select few chosen people would be brought," he said.

"It's alleged [in the television documentary] that people would be surrounded by groups of followers and beaten, and one 70-year-old man died some time after one of these alleged attacks.

"Some people are drawing a connection between that violence and his eventual passing."

Beatings common in church, Ms Lee says

The ABC understands the dead man is the father of Arum Song who lived with his family in Sydney for more than 20 years.

He worked in the IT industry before being recruited to Grace Road while living in Australia sometime around 2012.

Mr Song is interviewed in the documentary. He shows little emotion about the death of his father and says the cause was liver failure, not related to his time as a member of the Grace Road Church.

Ms Lee said she did not witness violence herself but other church members told her it was common.

"They beat you to a pulp," she said.

Grace Road operates about 60 businesses in Fiji including restaurants, farms and construction companies that have won government building contracts.

Grace Road has opened a chain of restaurants across Fiji. ( Facebook )

Power said the South Korean documentary includes allegations of labour exploitation.

"They say they weren't paid, they were treated as slaves, there's one person on film who claims they would work 14 hours a day starting at 5:30am and then when people started to physically break down they would be sent back to Korea," he said.

While Fiji police are continuing to investigate the church, in cooperation with South Korean authorities, the Fiji Government has told local media there was no need to investigate the business group's labour practices.

But the leader of the opposition National Federation Party, Biman Prasad, said there needed to be a full public inquiry on how Grace Road managed to get licences to operate.

"Unless the report of the investigation is laid out to the public there will always be suspicion as to how they were able to get in to all these different businesses and how they are getting government contracts," he said.

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Church ambitions to reach high levels of government

Ms Lee added that the group has ambitions to be highly influential in Fiji.

"The church members told me their plans and how they wanted to get Daniel Kim to a high position in the Government so they can have more freedom to expand," she said.

Mr Kim is the son of the Grace Roads founder. According to South Korean media he is wanted for questioning in South Korea.

Ms Lee said she was hopeful a conviction for the founder could mean the end of the church and its operation in Fiji.

"I really just want her behind bars and I want people to know this is insane and this has to stop," she said.

The ABC received no response to requests for comment from the Fiji Government, the South Korean consulate in Fiji and the Grace Road Church.

Grace Road has previously rejected allegations of wrongdoing.