That could lead to chaos at inoculation centres - and possibly help the virus spread further - as people horrified by COVID-19 patients' struggle for hospital beds and medical oxygen rush to seek immunity, government officials warn privately.
India has the world's biggest vaccine-making capacity, but has decided to delay big exports for now to focus on its own needs.
Still, supplies are already running short even for currently prioritised recipients over 45 years old.
"Eligibility doesn't guarantee availability," said a senior government official who declined to be identified.
"There are fears that the entire infrastructure will collapse but at this point all channels are being opened to ramp up supplies from other countries ... India needs a lot of help to deal with this crisis."
India is currently administering about 3 million doses a day, above the daily production of about 2.5 million and using existing inventories to fill the gap. Many states have reported they are out of stock.
Another government official said on the vaccination outlook: "(There will be) nothing dramatic by May, but more cases and deaths."
India recorded the world's highest daily tally of 314,835 infections on Thursday, taking its total to nearly 16 million, around 185,000 of whom have died.
The health ministry did not immediately respond to a request for comment on vaccines.
India has also urged Pfizer , Moderna and Johnson and Johnson to provide it with vaccines. Pfizer said it was talking to the government, while J&J has sought approval to do a small local trial but has not made any plans to sell it. Moderna has not commented.
Of the three, only J&J has a local production partner.
At the current rate of immunisation, using the AstraZeneca shot and homegrown Covaxin, it will take India more than two years to cover 70% of its 1.35 billon people, said Ramanan Laxminarayan, founder of the Center for Disease Dynamics, Economics & Policy in Washington and New Delhi.
"India has to produce at least 12 million doses for its own consumption every day," he said.
It has administered more than 131 million doses so far, the highest in the world after the United States and China. That, however, is lower than many richer countries per capita.
While India was initially fighting public hesitancy over vaccines, which partly led to it exporting millions of doses, the situation is completely the opposite now.
"Hundreds of people come to take vaccines, but every day they distribute only 100 coupons due to limited supply," said 45-year-old Santosh Pardeshi, who runs a laundry shop in the western district of Satara.
"I didn’t get a coupon the first day so the next day, I reached the centre at 6 a.m., stood in a queue for five hours and managed to get my first dose."
A senior Satara health official said the district had the capacity to administer 50,000 doses a day, but supplies were only half that.
"All vaccination centres are now crowded and in some places people get tired standing in queue and start arguing with our staff," said the official, who declined to be identified for speaking without permission from his superiors.
"The crowd will rise further from May 1 ... unless they increase supplies, it would be difficult to manage the crowds. We may have to take the help of police."
(Reporting by Krishna N. Das in New Delhi, Rupam Jain in Panjim and Rajendra Jadhav in Satara; Additional reporting by Neha Arora in New Delhi; Editing by Kim Coghill) ((Krishna.Das@tr.com; +91 987111 8314;))