Police have prevented the five-year-old Indian boy, who sparked controversy when he became the world's youngest marathon runner, from embarking on his next feat, a 500km (310 miles) walkathon in eastern India.

Officers lined the sun-scorched road in Orissa's capital, Bubaneshwa, yesterday to block Budhia Singh's path, citing a government order that declared the child's 65 km run last year to be torture.

"We have an order that Budhia Singh should not be allowed to participate in the proposed walkathon,'' police superintendent Amitabh Thakur told reporters as temperatures hovered near 40 degrees.

Budhia, who is known as "marathon boy", had been attempting a 10-day trek from the capital of eastern Orissa state to Calcutta in neighbouring West Bengal.

As police moved in, a small crowd of the boy's supporters unfurled homemade banners, chanting "Long Live Budhia", and started a sit-in. The boy's coach and foster father, Biranchi Das, said he would file an appeal with the local court.

Budhia was thrust into the spotlight after he clocked up an uninterrupted 65 km in seven hours and two minutes in May last year, running straight into the Limca Book of Records (India's equivalent of Guinness World Records).

Initially touted as a mini-Forrest Gump and India's next sporting hero, he appeared in television commercials and toured the country in scenes reminiscent of a Victorian travelling circus. But the mood swiftly changed after protests from child rights activists. He was subjected to a series of tests by state doctors who declared him undernourished, anaemic and under cardiac stress.

Budhia's story is as extraordinary as his ability to run. He grew up in a slum with his mother, who made a living washing dishes. She sold him when he was three to a street hawker for the equivalent of ยฃ10 as she could not afford to feed him and his sisters after her husband died.

Soon afterwards Mr Das, a local judo instructor, spotted Budhia misbehaving during training and set him to run around the track as punishment. He then went off to work and, so the story goes, forgot about him. When he returned five hours later the boy was still running: "I was amazed," he recalled. "I knew he was something extraordinary."

Mr Das says he has Budhia's best interests at heart and just wants to train him for the 2016 Olympics.