A Chinese factory worker says walking in huge iron shoes weighing more than 200 kilograms each can cure back pain, but faces hefty competition in his bid to build the country's heaviest footwear.

"I've been walking with iron shoes for seven years," said Zhang Fuxing, before strapping two crudely-welded iron blocks to his feet.

"After they reached 400 kilograms (882 pounds), I felt very proud. Next spring I plan to add 50 kilograms."

Zhang took a deep breath before each wrenching step in the towering footwear, with every impact leaving him struggling for balance.

It took him over a minute to take 10 paces, but he claims to walk up to 15 metres each day in the shoes, which he has gradually increased in weight, and touts them as a cure for back pain and hemorrhoids.

Zhang, 52, credits his ability to move the shoes -- which he leaves outdoors, safe in the knowledge that they are close to impossible for most people to lift -- to the Chinese spiritual martial art Qigong, said to involve controlling the flow of supposed bodily energies.

"It's not strong muscles that make you able to walk like this, the power comes from internal organs," he said, adding: "When you walk with your heart it will work."

Zhang believes his shoes to be the heaviest in China, but admits that competition from a number of other eccentrics renders his claim uncertain.

One of two Chinese iron shoe wearers to share a Guinness World Record for walking 10 metres backwards in heavyweight iron boots is Zhang Zhenghui from Changsha. According to a 2010 report by the official Xinhua news agency he has gold-painted shoes weighing more than 200 kilograms.

Lai Yingying, an entertainer from Fujian in the east, was shown by state broadcaster CCTV wearing shoes tipping the scales at a total of 300 kilograms.

A runner, Liu Mei, took to exercising in metal footwear after growing bored of tying sandbags onto his trainers, the state-run China News Service reported, and challenged other exponents to compete for the title of "Iron Shoe King".

His call "hit the world of eccentric stunt people like a tidal wave", the report said, but there is no record of the contest having taken place.

Zhang Fuxing -- who runs a workshop making machine parts -- says he was inspired by one of these pioneers. "I saw someone wearing iron shoes on TV. They said it was good for the heart and bones," he said.

At the time Zhang was suffering from back pain "so bad that I couldn't bend over to wash my face", but claims his symptoms disappeared just months after donning the footwear, an experience which left him wanting to share them with a wider audience.

He now manufactures a range of weighted metal footwear, which users strap over their existing shoes, in a small factory near his hometown in the northern city of Tangshan, and sells them online.

A snazzy red pair weighing 10 kilograms each costs 550 yuan ($90), while the heaviest 60 kilogram boots sell for 1450 yuan.

He claims to have sold several hundred pairs, including at least 10 to his neighbours, several of whom gathered around on a chilly morning to watch Zhang take his wobbling steps.

"We've all worn his iron shoes, it makes your legs feel better," said Chen Guanghua, a woman in her sixties. "We can't all play badminton, but anyone can wear shoes."