“The entire country will be in lockdown, total lockdown,” said Prime Minister Narendra Modi in a Tuesday address to the nation that has so far reported 519 coronavirus cases and nine deaths. “To save India, to save its every citizen, you, your family…every street, every neighborhood is being put under lockdown.”

Modi gave the world’s second-most-populous country a four-hour heads-up; police started enforcing the measure on Wednesday by arresting hundreds of people across the country for leaving their homes. The last-minute nature of the order caught the nation off-guard, causing the world’s largest COVID-19 lockdown to get off to a rocky start.

Lockdown trend

With the lockdown, India is following in the footsteps over a dozen other countries that have announced nationwide quarantine measures in response to the coronavirus pandemic, which has infected over 471,000 people around the world and killed upwards of 21,000, according to Johns Hopkins University.

The size of India’s population makes the scale of its lockdown unprecedented. Even in China, only the city of Wuhan and its surrounding area, the epicenter of the outbreak, were put under complete lockdown.

Modi communicated the lockdown on Tuesday on television and online, yet news of the drastic measure didn’t reach everyone, as news reports on Wednesday said some residents were confused as to why so few people were in the streets.

Economic impact

The lockdown is expected to devastate India’s economy.

The nation’s air travel industry, which is enduring a grounding of all domestic flights, is bracing for a loss of between $3.3 billion and $3.6 billion from April to June, according to CAPA India, an aviation consulting firm, Fortune India reports. India’s major carriers, such as Air India and IndiGo, may weather the lockdown with deeper cash reserves and potential financial assistance from the government, but smaller airlines might not survive.

“Although it is too early to come to a firm conclusion, what emerges on the other side may be a smaller, consolidated industry,” said CAPA India.

The coronavirus pandemic may prove a major setback to India’s hopes of becoming a global aviation powerhouse. India’s domestic airline industry represented the fastest-growing market in the world for four straight years until 2019, according to the International Air Transport Association.

India’s measures also pose a threat to the nation’s information technology sector, whose systems are vital to global commerce. India controls more than half of the world’s IT outsourcing market; its share of the industry serves over three-quarters of Fortune 500 companies and contributes roughly $58 billion a year to U.S. GDP.

With its work product based online, the IT industry is theoretically well-suited to shift to working from home, yet the lockdown has sent industry leaders in India scrambling. Some told Reuters they were unprepared for the rapid shift from office to home, citing various challenges, from a lack of equipment to regulations and privacy, as employees can often access projects only through secure, in-office networks.

“These days the challenge is not really the technology, the challenge is the regulations, and, in case something goes wrong, who’s going to take the responsibility,” a top human relations executive at an Indian IT firm told Reuters.

E-commerce emergency

Meanwhile, a field that should benefit from the lockdown—the country’s booming e-commerce sector—is also running into roadblocks.

The central government exempted e-commerce platforms from lockdown measures, yet some firms have reported snags at the local level.

BigBasket, India’s largest online supermarket, told its customers on Tuesday that the company was “not operational due to restrictions imposed by local authorities on the movement of goods in spite of clear guidelines provided by the central authorities to enable essential services.”

“We hope things will improve soon,” T.N. Hari, a senior executive at BigBasket, told Reuters on Monday.

Other major players like Amazon and the Walmart-owned Flipkart, which together control roughly 60% of India’s e-commerce market, had to temporarily suspend operations on Tuesday because of the lockdown restrictions. Later that day, Amazon announced that during the lockdown it would deliver only essential services like groceries. On Wednesday, Flipkart followed suit, yet there were still reported incidents of local authorities blocking deliveries of essential goods.

There are growing calls for a lockdown similar to India’s in countries like the U.S. Mass quarantines—like that of Wuhan and its surrounding area—have proven effective in controlling the spread of coronavirus, but the sheer scale of India’s effort makes it the ultimate lockdown test.

More coronavirus coverage from Fortune:

—Will ‘The Great Cessation’ be worse than the Great Recession?
—The U.S. needs more ventilators. Why can’t it make them in time?
—Which stores are open—and closed—during the coronavirus pandemic in the U.S.?
—College students struggle to find housing as the coronavirus pushes them off campus
—How to upgrade the background of your video chats
—IBM and The Weather Channel debut coronavirus map
—Listen to Leadership Next, a Fortune podcast examining the evolving role of CEO
—WATCH: World leaders and health experts on how to stop the spread of COVID-19

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