The leader of a New York City separatist group whose church used illegal tithes to swindle members out of millions of dollars has died.

Jermaine Grant, leader of the separatist group Israelite Church of God in Jesus Christ, based in the Manhattan neighbourhood of Harlem, was sentenced to 18 months prison after he admitted to spending church funds on personal expenses.

Grant's prison term was scheduled to begin later this month, however he died on April 1 after a brief illness.

Jermaine Grant, leader of New York separatist group Israelite Church of God in Jesus Christ, has died. (YouTube)

Grant's lawyer, Gerald Lefcourt, would not confirm whether his death was related to coronavirus.

However, church leaders later revealed on social media that Grant died from the virus.

"It is a tremendous loss —no question — and unfortunately due to the current restrictions put in place due to the coronavirus, we are prevented from coming together to comfort each other and say goodbye as we so desperately desire to do," church leaders said in a letter to followers.

According to court papers, Grant and church treasurer Lincoln Warrington used money from the Israelite Church of God in Jesus Christ to buy property, vehicles, trips and private-school tuition.

Grant and Warrington diverted more than $2 million from the church and failed to report more than $5 million in income.

Prosecutors said Grant had his children chauffeured to school every day in a Mercedes-Benz paid for with funds from a church bank account.

Israelite members have taken to social media to express their hurt but said that Grant's death revealed a certain amount of karma as he "perpetuate[d] lies in the name of God".

"I feel bad for those affected by his death," said former congregation member Barry Pugh, a whistle-blower who was prepared to testify for prosecutors.

"He lied to the congregation. Everything he did afterward was to lie and deceive the congregation."

Churchgoers revealed that crates with contents unknown to them were stacked ceiling high, guarded by 24-hour security.

An FBI raid of the Harlem church in 2018 uncovered crates full of money, the product of mandatory monthly 20 per cent tithes which is double the biblical requirement.

According to congregation members, church membership required a monthly payment plan and attendees had to hand in their mobile phones at the door.

Biblical brainwashing saw attendees swear devotion to Grant at the door, who called himself the "God-sent comforter".

The Israelite Church has been classified as a black nationalist hate group according to the Southern Poverty Law Centre.

The Centre that monitors hate groups said the Harlem church preaches a black Jesus will return to earth to enslave and kill white people.

The church was also a regular place of worship for the gunmen behind the anti-sematic shooting spree in Jersey City late last year.