A small group of super-spreaders were responsible for almost two-thirds of India's coronavirus cases, according to new research into how the disease spread in the world's second-most populous nation.

India has officially recorded 6.3 million cases so far -- second only to the United States -- and more than 98,000 deaths.

But the study, published in the journal Science on Wednesday, found that 70 percent of infected people across the country did not spread the disease to anyone else. 

By contrast, eight percent of all people carrying the virus were responsible for 60 percent of new infections.

The study also found that children under the age of 14 appeared to be more efficient spreaders of the virus.

"The findings indicate that... not all individuals transmit identically and also that children are potentially important in the transmission chain," the study's lead author Ramanan Laxminarayan told AFP.

Researchers studied transmission of the virus among more than half a million people exposed to 85,000 confirmed cases in India's southern Andhra Pradesh and Tamil Nadu states in August. 

India's response to the coronavirus pandemic has been severely hampered by its chronically underfunded healthcare systems. 

The country has gradually lifted a strict lockdown imposed in March to revive a national economy battered by the outbreak, even as infections steadily climb.