AHMEDABAD: Construction was set to begin in India on Thursday for the world's tallest statue, which will stand twice the size of the Statue of Liberty and be made out of melted-down metal and farming equipment.

The tribute to Sadar Patel, the first home minister of independent India who was nicknamed “Iron Man”, is set to rise 182 metres from a rocky river island in western Gujarat state.

Once completed it will be the world's biggest, more than four times higher than the statue of Christ the Redeemer in Rio de Janeiro.

Opposition leader Narendra Modi, the prime ministerial candidate for the Bharatiya Janata Party (BJP), was to lay the foundation stone on Thursday, Patel's birthday.

He has called on farmers to donate a piece of iron for the “Statue of Unity” which will stand atop a huge stone plinth.

“I want iron pieces from your villages,” Modi said in June as he launched the project at an agricultural summit. “But we do not want any piece of iron, we want pieces of iron from tools which a farmer has used in farming.”

A collection drive by state officials covering nearly 700,000 villages across the country will begin after Modi lays the foundation stone in Kevadia, about 170 kilometres from Gujarat's biggest city Ahmedabad.

The total cost of the project is estimated at 25 billion rupees ($300 million) and will be funded with public funds and private donations, state officials say.

The collected metal will be melted down and used in the statue, which is being built by Turner Construction, the company behind the world's tallest building, the Burj Khalifa in Dubai.

The memorial has strong political undertones as it honours an independence hero who spent his life in the Congress party, Modi's main rival in national elections due by May next year.

In what is already a highly personal campaign, Modi suggested earlier this week that Patel, who is from Gujarat, would have made a better leader than India's first prime minister Jawaharlal Nehru.

This was a provocative dig at India's modern-day Gandhi political dynasty, led by Congress chief Sonia and her son Rahul, who are descended through Nehru.

The family has ruled for most of India's post-independence history.