Christian leaders have been paying tribute to Operation Mobilization founder George Verwer, who passed away on Friday. He was 84.

OM USA announced his death with "profound sadness" while giving thanks for his enormous legacy.

"Through our tears, we give thanks for all George has meant to us and take comfort that he is with Jesus, whom he loved and served faithfully," it said.

Evangelical Alliance CEO, Gavin Calver, said he was "very sad" to hear of Verwer's passing.

"He was a trailblazer, a mentor to many and an evangelistic giant in his day. He will be hugely missed but his legacy will live on in the lives of so many globally," he said.

"I am honoured to have known him. May he rest in peace and rise in glory."

Franklin Graham, son of the late evangelist, Billy Graham, called Verwer a "giant in the world of evangelism".

"I've never known anyone who kept a schedule like him—he would preach the Gospel multiple times a day almost every day somewhere around the world," he said.

"George's life was transformed after his neighbor, Dorothea Clapp, gave him a copy of the book of John from the Bible and put him on her prayer list, which she called her 'Holy Ghost hit list.'

"George then surrendered his life to Christ at the age of 16 at a meeting in Madison Square Garden where my father, Billy Graham, preached.

"Does prayer work? You bet it does! George was a fervent witness for Christ, and it is said that within a year, 200 of his classmates had become Christians—and his passion for seeing souls saved never faded.

"Operation Mobilisation continues to touch the world with the Good News of Jesus Christ. I have been with him on several occasions and always appreciated that he came to Boone to see me a number of years ago and brought his father. George Verwer was used mightily by God and will be greatly missed."

Andy Frost, director of Share Jesus International, gave thanks for Verwer's life and legacy. 

"A life well lived. The baton is with us," he said. 

The Gospel Coalition said, "George Verwer was a man who never got over the goodness of the good news. His passion was to see all the peoples of the world finally and eternally glad in Christ."

Verwer died peacefully at home surrounded by his family. He is survived by wife Drena and children, Ben, Daniel and Christa. 

In his final video blog post earlier this month, he said he hoped his greatest legacy would be "a revolution of love ... combined with reaching people" and "combined with prayer". 

"There are hundreds and hundreds and millions of people who have not yet been reached," he said.