Several Indian states have run out of Covid-19 vaccines a day before a planned widening of a nationwide inoculation drive, authorities said on Friday, as new infections in the crisis-hit country surged to another daily record.

India reported 386,452 news cases in the past 24 hours, while deaths from Covid-19 jumped by 3,498 over the last 24 hours, according to health ministry data.

However, medical experts believe actual Covid-19 numbers may be five to 10 times greater than the official tally.

Explainer: What we know about the Indian variant as coronavirus sweeps South Asia

India has added about 7.7 million cases since the end of February, when its second wave picked up steam, according to a Reuters tally. In contrast, it took India nearly six months to add the previous 7.7 million cases.

The world's second-most populous nation is in deep crisis, with hospitals and morgues overwhelmed by the pandemic, medicines and oxygen in short supply and strict curbs on movement in its biggest cities.

India is the world's biggest producer of vaccines but does not have enough stockpiles to keep up with the second deadly Covid-19 wave, despite Prime Minister Narendra Modi's government planning to vaccinate all adults starting May 1.

Only about 9 per cent of India's 1.4 billion people have received a vaccine dose since January.

“I registered to get a slot 28 days before, but now they are saying there are no vaccines,” Twitter user Jasmin Oza said in a video post.

India had originally planned to vaccinate only 300 million of its highest-risk people by August, but widened the target due to the rise in cases.

However, its two vaccine producers were already struggling to increase capacity beyond 80 million doses a month due to a shortage of raw materials and a fire at the Serum Institute, which manufactures AstraZeneca's vaccine in India.

Inoculation centres in Mumbai will be shut for three days starting Friday because of the shortage of vaccines, authorities said.

In the southern state of Karnataka, home to the tech hub of Bengaluru, the state's health minister said Karnataka's vaccination drive for adults will not begin on May 1.

“The state government has not received any information from companies about when they will be able to supply these vaccines,” said Health Minister K Sudhakar.

World sends medical aid

In Modi's home state of Gujarat, officials said vaccination for the 18-45 age group is expected to start in a fortnight, as the state expects to receive vaccines by then.

“We will begin vaccinating those above 18 when we have the vaccine stocks. We are working very hard to get the vaccines, and I am confident we will be able to start the vaccination within the next 15 days," the state's Chief Minister Vijay Rupani said.

Officials in the eastern state of Odisha said they hoped to start vaccinations on Monday, if vaccine stocks arrive.

Modi is scheduled to meet cabinet ministers on Friday as the wave of infections cripples the nation's health system and threatens to impact major businesses.

Absenteeism in offices and industries is growing with staff falling sick or taking leave to tend to sick relatives.

World aid has started arriving in India as it struggles to combat what has been described as a humanitarian disaster.

The first US flight carrying oxygen cylinders, regulators, rapid diagnostic kits, N95 masks and pulse oximeters arrived in the Indian capital Delhi on Friday.

“Just as India came to our aid early in the pandemic, the US is committed to working urgently to provide assistance to India in its time of need,” US Secretary of State Antony Blinken said on Twitter.

“Today we are proud to deliver our first shipment of critical oxygen equipment, therapeutics and raw materials for vaccine production.”

The United States will send more than $100 million in medical aid, including 1,000 oxygen cylinders, 15 million N95 masks and 1 million rapid diagnostic tests. It also has redirected its own order of AstraZeneca supplies to India, to allow it to make more than 20 million doses.

Shipments from other countries continued to pour in, with a third one from the United Kingdom reaching earlier in the day. Romania and Ireland also sent supplies late on Thursday.

Two more weeks of oxygen crisis

India's severe medical oxygen supply crisis is expected to ease by mid-May, a top industry executive told Reuters, with output rising by 25pc and transport infrastructure ready to cope with a surge in demand.

India will receive a first batch of Russia's Sputnik V vaccine on May 1. Russia's RDIF sovereign wealth fund, which markets Sputnik V globally, has signed deals with five Indian manufacturers for more than 850 million vaccine doses a year.

Prominent US disease modeller Chris Murray, from the University of Washington, said the sheer magnitude of infections in India in a short period of time suggests an “escape variant” may be overpowering any prior immunity from natural infections in those populations.

“That makes it most likely that its B.1.617,” he said.

But Murray cautioned that gene sequencing data on the coronavirus in India is sparse, and that many cases are also being driven by the UK and South African variants.

Carlo Federico Perno, Head of Microbiology and Immunology Diagnostics at Rome's Bambino Ges Hospital, said the Indian variant couldn't alone be the reason for India's huge surge, pointing instead to large social gatherings.

Modi has been criticised for allowing massive political rallies and religious festivals which have been super-spreader events in recent weeks.