A 92-year-old US grandmother has become the oldest woman to finish a marathon.

A smiling Harriette Thompson, aged 92 years and 65 days, was cheered by dozens of onlookers and supporters as she completed San Diego’s Rock n Roll marathon in seven hours, 24 minutes and 36 seconds.

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Speaking to her hometown newspaper, the Charlotte Observer, Thompson said she felt “a little stiff” after the race.

“I was really tired at one point. Around mile 21, I was going up a hill and it was like a mountain,” she said.

“I was thinking, ‘This is sort of crazy at my age’. But then I felt better coming down the hill. And my son Brenny kept feeding me all this wonderful carbohydrates that kept me going.”

The previous oldest woman marathon runner was another American, Gladys “Gladyator” Burrill, who was 92 years and 19 days old when she did the Honolulu event in 2010.

Thompson participated in the marathon to raise money for cancer research, a disease she has herself survived.

The grandmother to 10 grandkids also completed the race last year with a time of seven hours, seven minutes and 42 seconds.

The oldest male marathon runner is Fauja Singh, who was 101 when he retired from racing in 2013.