Tens of millions of people have reportedly formed an 18,000km long human chain in the northern Indian state of Bihar to raise awareness about the environment and social justice.

Video recorded in the city of Chapra shows scores of people out in the streets linking arms and and supporting the cause in the event organised by the local state government.

Multiple local reports claimed 50 million people took part in the human chain to raise awareness about environmental conservation and "social ills," with some holding signs about addiction and disclaiming child marriage.

The official Twitter account of the United Nations Environment Programme tweeted: "An estimated 50 million people in India's Bihar State made a massive human chain stretching over 18,000 km yesterday. Why? To raise awareness that we are in a #ClimateCrisis and to show resolve to protect our planet."

The state has organised similar events for such causes in the last three years.