India's Prime Minister Narendra Modi on Tuesday night declared a 21-day nationwide lockdown to stop the spread of coronavirus amid fears that the nation of 1.3 billion people could be on the brink of a massive outbreak.

"Currently, India is at a stage where our current actions will determine how much we are able to minimize the impact of this disaster," Modi said in a televised address.

If India does not "handle these 21 days well, then our country... will go backwards by 21 years," warned Modi.

India has experienced a spike in COVID-19 cases in recent days. On Thursday, the number of confirmed cases was over 560, according to the Johns Hopkins University coronavirus resource center. More than 10 people have died.

A hidden epidemic in India?

However, public health experts are concerned that the relatively low number of official cases in India reported by the Ministry of Health belies the actual scale of the outbreak.

Experts warn that without mass-testing, India might not be able to detect and mitigate community transmission of COVID-19. There are fears that community transmission of the virus has already begun, as cases are being reported among people with no history of foreign travel or contact with people who have traveled abroad.

"Early and mass testing make all the difference because, in many cases, coronavirus can be asymptomatic. To detect community transmission, we have to test many more people with flu symptoms, even if they will turn out to be infected with seasonal flu and not the coronavirus," said T Sundararaman, the former director of India's National Health Systems Resource Centre, an advisory body to the Indian Ministry of Health.

The health ministry recently approved 12 private COVID-19 testing labs, and there are 15,000 collection centers, according to a government press release.

However, the effectiveness of the testing system remains unproven, and the testing rate in India is low.

As health officials begin to test more people in more cities, the numbers of confirmed cases is expected to rise rapidly.

"The infection is simmering and is waiting to explode. The official numbers that are announced right now are only the tip of the iceberg," Arvind Kumar, a lung surgeon at Sir Ganga Ram Hospital in Delhi, told DW.

Indian epidemiologist Jayaprakash Muliyil issued a dire warning recently, estimating that up to 55% of India's population could contract COVID-19.

Other estimates of the contagion's spread in India, applying mathematical models used in the United States and Great Britain, indicate India could have 300 million COVID-19 cases by July.

Can India 'flatten the curve?'

If these dire predictions of rising COVID-19 caseloads come true in India, the surge would overwhelm the country's already underfunded healthcare infrastructure.

To stem the outbreak, India has several measures in place combined with the nationwide lockdown. Authorities are tracking people who have returned from abroad. According to media reports, authorities can seal off houses and enforce quarantine if someone breaks protocol.

Any healthcare system facing the COVID-19 pandemic depends on the number of cases being spread out over a longer period of time. The logic behind nationwide lockdowns and quarantines is to slow the transmission rate and give hospitals a chance to treat as many patients as possible.

Right now, India needs time to obtain more coronavirus testing kits and ventilators.

"Many patients have to be put on breathing support and India's hospitals are not equipped with enough ventilators," said Mukesh Muki, a doctor at a hospital in southern city of Bangalore.

Officials at the Indian Council of Medical Research told DW that a million coronavirus test kits from Germany have been ordered to meet the demand.

"There is no cause for panic. We already have over 100,000 testing kits and we will procure more kits soon," Lav Agarwal, the health ministry's joint secretary, told DW.

Health ministry figures show there are around 30,000 ventilators in India right now, with 800 alone in Mumbai, the worst-affected city. Procuring more is complicated by supply line disruptions due to the travel ban.

Besides ensuring supplies, getting people to comply with quarantines and lockdowns is another problem.

"The biggest concern in combating coronavirus is people's mentality. People just refuse to take precautions or take this pandemic seriously," said Muki.

"Though the government was prompt in responding to the situation, we could have broken the chain of transmission by imposing a lockdown much earlier," Prashant Kashyap, managing editor at the mass circulation Dainik Jagran newspaper, told DW.

"Before the lockdown, everyone was active in their neighborhood and out in the streets."

Indians prepare for the worst

Essential services like grocery stores, banks and pharmacies will remain open, although they are encouraged to increase home delivery services.

Nevertheless, as the lockdown began Wednesday, people across the India scrambled to markets, pharmacies and stores to stock up on supplies.

Except for a few public-run buses running on select routes, most public transport in India has been halted. As states shut their borders, long lines of trucks carrying milk, fruits and vegetables crawled on several highways.

Online grocers said they were struggling to maintain their supply chains.

"I have been waiting for two hours to buy milk and some fruits. This is horrible. People have been hoarding leaving us with nothing," said Priya Kapoor, a housewife in Delhi.

Wage laborers are hit especially hard by the lockdown. Many are set to lose their jobs or get evicted from their homes. Although the government has called for "proactive measures" to protect laborers, including a government pay out, workers said they are not sure when they will be paid.

"I really don't know what to do. My family has been waiting for me to come home for three days. But I have no choice but stay in Lucknow with no income," said Rajeev Paswan, a construction laborer.

The mass movement of laborers from cities to the countryside, particularly in the agricultural belt in the states of Uttar Pradesh, Bihar and West Bengal, also poses a public health risk, as many may unknowingly be carrying the coronavirus.

"India has different layers of awareness about the coronavirus pandemic. While one part of India is aware and has taken precautions, the majority of people are still unaware. It's difficult to lock down people living in villages. It is now the harvesting season. A farmer doesn't work like a corporate executive. His work can't be done indoors," said journalist Kashyap.

"Community transmission is now inevitable and the rural medical infrastructure is absolutely unequipped to handle an outbreak," he added.

Baldev Rai, a shopkeeper and tea seller in Gurugram near New Delhi said he doesn't know about the symptoms of coronavirus or its mode of transmission. "I just want to go back to the farmland in my hometown," he told DW.