India’s 1.3 billion people asked to stay home for 21 days as the biggest single lockdown of coronavirus pandemic begins.

Indians crowded grocery stores and pharmacies on Wednesday in a struggle for essential items after Prime Minister Narendra Modi ordered a total lockdown for three weeks to fight the coronavirus pandemic, one of the toughest such measures worldwide.

India’s tally of 536 cases and 10 deaths is dwarfed by China, Italy, and Spain, but Modi and health experts have warned that the nation of 1.3 billion people faces a tidal wave of infections if harsh steps are not taken.

People in the key cities of New Delhi, Mumbai and Bengaluru rushed to stock up after Modi decreed the shutdown in a speech televised nationwide, barely four hours before it took effect.

Everything, except for essential services like supermarkets, was shuttered.

As states shut their borders, long queues of trucks carrying milk, fruits and vegetables snaked down highways, even though Modi said essential services would be maintained countrywide.

“There are no clear instructions, police are telling us to close down the shop,” said Ram Agarwal, a grocer in New Delhi swamped by people looking to buy dry food supplies and milk.

Al Jazeera’s Elizabeth Puranam, reporting from New Delhi, said Wednesday morning was quieter after panic buying immediately after Modi’s address on Tuesday night.

“Delhi Chief Minister Arvind Kejriwal in a news conference said that people crowding to buy essential commodities defeated the purpose of the lockdown,” she said.

Normally bustling railway stations in New Delhi were deserted. “Delhi looks like a ghost town,” said Nishank Gupta, a lawyer. “I have never seen the city so quiet before.”

The government said on Wednesday that it is banning the export of hydroxychloroquine and formulations made from the medication, as experts test the efficacy of the drug in helping treat patients infected with COVID-19.

Hydroxychloroquine, a malaria drug, is among the medications that are being tested, as a potential treatment for patients with the disease.