India’s toll from the coronavirus surged past 200,000 on Wednesday, the country’s deadliest day, as shortages of oxygen, medical supplies and hospital staff compounded a record number of new infections.

The second wave of infections has seen at least 300,000 people test positive each day for the past week, overwhelming healthcare facilities and crematoriums and fuelling an increasingly urgent international response.

The last 24 hours brought 360,960 new cases for the world's largest single-day total, taking India's tally of infections to nearly 18 million. It was also the deadliest day so far, with 3,293 fatalities carrying the toll to 201,187.

Experts believe the official tally vastly underestimates the actual toll in a nation of 1.35 billion, however.

The world is entering a critical phase of the pandemic and needs to have vaccinations available for all adults as soon as possible, said Udaya Regmi, South Asia head of the International Federation of Red Cross and Red Crescent Societies (IFRC).

"This is both an ethical and public health imperative," he added. "As variants keep spreading, this pandemic is far from over until the whole world is safe."

Ambulances lined up for hours in the capital, New Delhi, to take the bodies of Covid-19 victims to makeshift crematorium facilities in parks and parking lots, where bodies burned on rows of funeral pyres.

Coronavirus sufferers, many struggling for breath, flocked to a Sikh temple on the city's outskirts, hoping to secure some of its limited supplies of oxygen.

Hospitals in and around the capital said oxygen remained scarce, despite commitments to step up supplies.

"We make hundreds of calls and send messages every day to get our daily quota of oxygen," Dr Devlina Chakravarty, of the Artemis hospital in the suburb of Gurgaon, wrote in the Times of India newspaper.

The Mayom Hospital nearby has stopped new admissions unless patients brought oxygen cylinders or concentrators with them, its chief executive, Manish Prakash, told television channel NDTV.

Delhi Chief Minister Arvind Kejriwal said people were falling sick more severely and for longer, stacking up the pressure.

"The current wave is particularly dangerous," he said.

"It is supremely contagious and those who are contracting it are not able to recover as swiftly. In these conditions, intensive care wards are in great demand."

Supplies incoming

Supplies arriving in New Delhi included ventilators and oxygen concentrators from Britain, with more sent from Australia, Germany and Ireland, while Singapore and Russia pledged oxygen cylinders and medical supplies.

"First shipment of oxygen generators from Taiwan to India is leaving this week," Kolas Yotaka, a spokeswoman for Taiwan President Tsai Ing-wen, said on Twitter. "We are all in this together."

Canadian Prime Minister Justin Trudeau committed $10m, adding on Twitter, "We stand ready to donate extra medical supplies, too."

Credit rating agency S&P Global said India's second wave of infections could impede its economic recovery and expose other nations to further waves of outbreaks.

The Asia-Pacific region, in particular, was susceptible to contagion from the highly infectious variants in India, given the region's low ratios of vaccination, it added.

Tech firms in the southern city of Bengaluru and elsewhere set up "war rooms" as they scrambled to source oxygen, medicine and hospital beds for infected workers and maintain backroom operations for the world's biggest financial firms.

Epidemiologist Bhramar Mukherjee called for much larger lockdowns to slow the spread.

"At this point, lives are so much more important than livelihoods," the University of Michigan professor said on Twitter. "Provide assistance to the poor, but please lock down and vaccinate."

Vaccinations in a national campaign begun in January have averaged about 2.8m doses a day since an April 5 peak of 4.5m, government data shows.

More than 121m people have received at least one dose, or about nine per cent of the population.

Later on Wednesday, India will allow all above 18 to register for vaccination, starting from May 1. About 800m are estimated to become eligible.

US President Joe Biden said he had spoken at length with Indian Prime Minister Narendra Modi on issues such as when the United States would be able to ship vaccines to the South Asian nation, and added that it was his clear intention to do so.

"I think we'll be in a position to be able to share, share vaccines, as well as know-how, with other countries who are in real need. That's the hope and expectation," he told reporters at the White House on Tuesday.