A 100-year-old British man is believed to have become the oldest person ever to complete a full marathon - after taking up running at the age of 89.

Fauja Singh, known as the 'Turbaned Tornado', took eight hours to cross the finish line in Sunday's Toronto marathon - more than six hours after Kenya's Kenneth Mungara won the event for the fourth straight year.

Although finishing 3,849th, Singh was "overjoyed" about beating his predicted time, his coach Harmander Singh told the Toronto Star.

The runner had set a goal of finishing the race in about nine hours.

"He's absolutely overjoyed, he's achieved his life-long wish," his coach said.

"He was so determined to finish the race. The challenge for him was to finish the race, not to finish the race fast.

"The crowd was most encouraging."

Fans cheered his accomplishment in newspapers and online, with the centenarian's achievement attracting 17,000 comments on Facebook.

Sunday's Toronto marathon was Singh's eighth.

He entered his first race at age 89 after losing his wife and child.

He hopes next to carry the torch at the 2012 Olympics in London.

ABC/AFP