New Delhi — India's government is facing criticism for the relatively low number of tests it's administered to detect cases of the new coronavirus, raising fears that tens of thousands of patients may be going undetected. India has tested only about 12,000 people so far, despite a capacity to test about ten times that many.

Only people who have traveled from the worst affected countries or come in contact with a confirmed case and shown symptoms after two weeks of quarantine are being tested — criteria that experts call "very narrow."

The World Health Organization has urged countries to test every suspect case, not just people with relevant travel or contact history.

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But many Indians with symptoms indicative of a possible COVID-19 infection, have been turned away from hospitals as they seek tests, and that is causing increasing fear in the world's second most populous country.

Bank clerks wearing a facemask amid concerns over the the spread of the COVID-19 coronavirus serve customers at a bank, in Bangalore on March 19, 2020. Getty

India has some of the most densely populated cities in the world, but has reported only four deaths and 173 confirmed cases of COVID-19 so far. Experts believe the low testing rate may be hiding thousands more patients from the data.

Professor Ramanan Laxminarayan, an epidemiologist and senior research scholar at Princeton University, told CBS News the actual number could be in "tens of thousands."

"The number of tests being done in India right now is grossly inadequate ... also because the criteria is narrow," Laxminarayan told CBS News. "India should be conducting at least 10,000 to 20,000 tests per day ... it has the capacity to conduct 100,000 tests per day."

"We have already wasted three weeks. We need to ramp up the testing," he said. "If we wait, things can get majorly out of control."

A report by Bloomberg on Tuesday cited multiple experts with similar concerns that India could become the next global hotspot in the pandemic, with a possible "avalanche" of new cases looming around the corner.

"That's not just possible, but most probable," said Laxminarayan, who was featured in a "60 Minutes" report last year explaining how antibiotic-resistant superbugs could become a bigger killer than cancer.

Promise to do better

Under the intense criticism, the Indian government has now said it will ramp up coronavirus testing by increasing the number of labs where the tests can be carried out, including by roping in private labs.

"By the end of this week, there will be 72 functional ICMR labs for COVID-19 testing and also 49 others in the government system. We are also in talks with 51 private laboratories… to start testing," Balram Bhargava, a secretary at the department of health research, told reporters Thursday.

The government had previously said it didn't want to "create unnecessary panic by allowing indiscriminate testing."

A member of the transgender community distributes free facemasks amid concerns over the spread of the COVID-19 disease at a market in Allahabad, India, March 19, 2020. Getty

While an increase in data will help build a more accurate picture of the outbreak in India, it may come too late to prevent the expected surge in new cases.

1-day lockdown

On Thursday, as a fourth death was reported, India escalated its restrictions on society aimed at curbing the spread of COVID-19. No international flights will be allowed to land in India for a week from Sunday. The country had already suspended visas for most countries.

The government has advised people over 65 and children under 10 to stay home, and asked private companies to ensure that any employees who can do their jobs from home, do so.

Several state and local governments have closed schools, colleges, shopping malls, public parks, and banned large gatherings.

There was speculation that Prime Minister Narendra Modi might announce significant new national measures Thursday, as other countries and cities around the world impose lockdowns.

Addressing his nation, he announced that a one-day curfew would be imposed on Sunday. Everyone in the country will be required to stay home between 7 a.m. and 9 p.m., apart from "those related to essential services."

He did not explain how ordering people to stay home for just one day might help slow the spread of the disease, but many saw it as a possible effort to prepare the nation for more lasting restrictions.

Modi did urge all Indians to stay home for all but essential needs, saying the "coronavirus has endangered humanity. It has affected more nations than the World War."

"I want to reassure that all steps are being taken to ensure that the supply of milk, medicines and food does not stop. Do not hoard, be sensitive towards the need of others," he said, adding a call for "the upper class" not to cut works wages if they are sidelined by the virus.

"Remember, they also have to take care of their family and protect them," Modi said.