India's confirmed coronavirus cases crossed the three million mark Sunday with nearly 70,000 new infections, as the disease continues to surge in the world's second most-populous nation.

The health ministry said 69,239 cases were detected on Sunday, with 912 deaths taking the total number of fatalities to 56,706.

Many experts say, however, that the real scale of the infection is much higher.

Authorities in New Delhi said last week that an antibody study in the megacity suggested more than a quarter of the capital's population had contracted the infection.

Indian Prime Minister Narendra Modi's government imposed one of the world's strictest lockdowns in late March that has been mostly eased in recent weeks.

But the epidemic has left Asia's third-largest economy reeling, and tens of millions of people have lost their jobs and livelihoods.

Individual states and cities have imposed localised lockdowns -- including Haryana and Punjab, where cases have spiked in recent weeks.

Previously the main hotspots have been the teeming megacities of New Delhi and Mumbai, home to some of the world's biggest slums.

"At the moment we are seeing a fairly sharp rise in cases overall for India," said K Srinath Reddy, of the non-governmental Public Health Foundation of India.