India's main opposition leader Rahul Gandhi has warned that unless the deadly second Covid-19 wave sweeping the country is brought under control it would decimate India as well as threaten the rest of the world.

In a letter, Gandhi implored Prime Minister Narendra Modi to prepare for another national lockdown, accelerate a country-wide vaccination programme and scientifically track the virus and its mutations.

Gandhi said the world's second-most populous nation had a responsibility in "a globalised and interconnected world" to stop the "explosive" growth of Covid-19 within its borders.