Seasonal flooding of the Ganges is flushing out shallow graves and exposing some of the hundreds of bodies that were buried by the river during India's recent Covid-19 surge.

Neeraj Kumar Singh, an official in the northern city of Allahabad, said that almost 150 bodies have had to be cremated in the past three weeks.

"We are not exhuming any bodies but only those which are floating up due to rising water levels are being cremated," he said.

"The area is spread over a kilometre (half a mile) and our guess is there are around 500-600 bodies buried," Singh told AFP.

"Every precaution is taken in dealing with the bodies while performing their final rites."

Most are believed to have died from coronavirus in April and May when India was hit by a spike in infections that overwhelmed hospitals in many areas.

Some families were unable to afford firewood for traditional Hindu cremations so bodies were immersed in the Ganges or buried in sandbanks adjacent to the river.

These are now becoming flooded because of annual monsoon rains swelling the river, washing away the sand and revealing the corpses.

The number of such graves has stoked suspicions that India's total deaths from the pandemic may be over a million, several times the official toll of almost 400,000.