The Indian state of Bihar has increased its Covid-19 death toll after the discovery of thousands of unreported cases, raising concerns that many more fatalities were not officially recorded.

The health department in Bihar, one of the poorest states, revised its Covid-19 fatality count to more than 9,429 from 5,424 a jump of more than 70 per cent.

Officials said the 3,951 unreported fatalities had occurred in May and reflect deaths reported at private hospitals, in transit to health facilities, under home isolation and those dying of post Covid-19 complications, AP reported.

Health experts say many Covid-19 fatalities remain unrecorded in India, more so during the latest surge in April and May, when hospitals ran unbearably full and oxygen supplies were low.