Tens of thousands of farmers drove a convoy of tractors festooned with brightly-coloured flags through the outskirts of India's capital of New Delhi on Tuesday, in a high-profile protest against controversial agricultural reforms.

Growers, angry at what they see as laws that help large, private buyers at the expense of producers, have been camped outside Delhi for almost two months.

Thousands more, steering tractors bearing the flags of India and farm unions, had streamed in from neighbouring states for several days ahead of the rally, planned to coincide with celebrations of Republic Day.

‘Our word should travel around the world, that we are fighting for our living,’ said Devinder Singh, a 36-year-old farmer from Punjab, seated on his tractor.

‘If we lose our farm land, how will we survive?’ he asked, as he waited at Singhu, one of the main protest sites.

The protests have so far been peaceful, and farm leaders have urged rally participants to refrain from violence.

Authorities used trucks to barricade the main route to the site, where hundreds of police, some armed with assault rifles, tear gas, and a water cannon, stood guard.

Although some protesters breached police barricades at Singhu and Tikri, another site, early on Tuesday, there were no immediate reports of violence.

Agriculture employs about half of India's population of 1.3 billion, and unrest among an estimated 150 million landowning farmers presents one of the biggest challenges to the authority of Prime Minister Narendra Modi since he came to power in 2014.

Nine rounds of talks between the government and the farmers' unions have failed to end the protests, with farm leaders rejecting the government's offer to delay the laws for 18 months, as they push for repeal.

‘The farm organizations have a very strong hold,’ said Ambar Kumar Ghosh, an analyst at the New Delhi-based Observer Research Foundation think-tank.

‘They have the resources to mobilize support, and to continue the protest for a long time. They have also been very successful in keeping the protest really focused.’

Police have allowed farmers to rally along approved routes on the outskirts of Delhi.

But the tractor march threatens to overshadow the annual Republic Day military parade in the centre of the capital on the anniversary of India's 1950 adoption of its constitution.

‘They could have chosen any other day instead of January 26 but they have announced now,’ Agriculture Minister Narendra Singh Tomar told media on Monday.

‘Conducting the rally peacefully without any accident would be the concern for farmers as well as police administration.’