NEW DELHI (REUTERS) - India, the country currently being hit hardest by the pandemic, on Tuesday reported its worst daily death toll, with large parts of the country now under lockdown amid a fast-rising second wave of infections.

The health ministry said 1,761 people had died in the past day, bringing India's toll to 180,530, still well below the 567,538 deaths reported in the United States, though experts believe India's actual deaths are far more than the official count.

The world's second most populous country is grappling with its biggest public health emergency after it lowered its guard when coronavirus infections fell to a multi-month low in February, health experts and officials say.

Several major cities are already reporting far larger numbers of cremations and burials under coronavirus protocols than official Covid-19 death tolls, according to crematorium and cemetery workers, the media and a review of government data.

The crisis in hospitals has left people fighting for beds, oxygen and medicines, and doctors said the shortages will inevitably lead to more deaths.

"The huge pressure on hospitals and the health system right now will mean that a good number who would have recovered had they been able to access hospital services may die," said Gautam I. Menon, a professor at Ashoka University.

On Tuesday, the health ministry reported 259,170 new infections, a sixth day over 200,000 and getting closer to the peak of nearly 300,000 seen in the United States in January.

Total coronavirus cases in India are now at 15.3 million, second only to the United States, with epidemiologists saying far more infectious new variants were one of the main factors behind the latest surge in cases.

Vaccinations drag

Opposition leader Rahul Gandhi - who has also addressed Congress party election rallies in recent weeks - said he had tested positive for the virus.

The hardest-hit western state of Maharashtra announced fresh curbs, restricting opening times for grocery shops and vendors to just four hours a day.

Further north, the capital city Delhi suffered a record overnight death toll following a surge in infections, and began a six-day lockdown late on Monday.

Media reports said the city's Chief Minister Arvind Kejriwal had gone into isolation after his wife tested positive.

People in Delhi and towns of the populous northern state of Uttar Pradesh put out desperate calls for help on Twitter, asking for assistance getting their families into hospitals.

Others reported dire shortages of oxygen and the anti-viral drug remdesivir.

Diagnostics firms in big cities were virtually overwhelmed by the numbers of coronavirus tests being sought, officials said.

Mr Manish Tewari, an opposition lawmaker, said on Twitter that a "monumental tragedy of epic proportions is unfolding across India. No hospital beds, no oxygen, no vaccination."

Stung by criticism that the government had failed its people, Prime Minister Narendra Modi ordered vaccinations on Monday for anyone above the age of 18 to be given from May 1.

So far, 109.6 million people have received a first dose, according to a government portal, a small portion of India's 1.3 billion population.

India's daily vaccinations peaked at 4.5 million doses on April 5, but have averaged about 2.8 million a day since, government data showed.

Diagnostics firms testing for coronavirus are nearing breaking point in cities like New Delhi and Mumbai as India battles its biggest surge in Covid-19 infections, which may worsen the crisis as many sick people can't get tested fast enough to isolate themselves.

"We can't cater to the demand," said Dr Vidur Mahajan of Mahajan Imaging in the Indian capital, who has temporarily shut two of his three sample collection points due to a backlog of pre-booked tests, and to prioritise testing for government hospitals.

Officials from four diagnostics companies, including Dr Mahajan, said samples currently being tested daily were between 300 per cent and 650 per cent higher than February, putting infrastructure and personnel under severe pressure.

Doctors and patients in New Delhi and financial hub Mumbai said it was taking between three to eight days to find slots for the highly accurate RT-PCR tests and get their results.

If sample arrivals rise further, by 25 per cent to 30 per cent," probably the testing facilities will crash, in terms of turn-around time at least", said Mr A. Ganesan, group vice-chairman of Neuberg Diagnostics, which runs 14 testing labs across India.

"We will have to turn back some of the patients without collecting their samples."

India's health ministry did not immediately respond to questions from Reuters.

The government said 1.5 million samples were tested on Monday (April 19), a jump from about one million at the start of the month.

With hospitals full and oxygen and medicines in short supply, several cities are reporting far larger numbers of cremations and burials under coronavirus protocols than official Covid-19 death tolls, according to crematorium and cemetery workers, media and a review of government data.

New Delhi resident Puneet Vig said it took several calls to four labs this week before he was able to book a test for his 62-year-old mother, who has been running a fever.

Her sample is due to be collected on April 24, with at least a couple of more days of delay expected till her results become available, he said.

"If you can't get a basic thing like testing done even in Delhi, it is very frustrating," Mr Vig said.

With test results often delayed, doctors said they were relying on CT scans and symptoms to treat patients.

"What is happening because of the delayed testing is that the circle of transmission is getting wider and wider," said Dr Ravindra Khade Patil of Sushrut Hospitals, on the outskirts of Mumbai.

"Without a test, the patient may not isolate and thus infect others."