Social distancing difficult in nations teeming with people.

JAKARTA, Indonesia — The Bangladeshi government this week ordered a nationwide shutdown to try to slow the spread of the coronavirus in a country considered at high risk because hundreds of thousands of overseas workers have returned home from Italy and other virus hot spots.

All businesses were ordered closed except food markets, pharmacies and other essential services, and people were told to stay indoors and keep a safe distance from each other.

But in Dhaka, a city of more than 10 million where the average home is less than 120 square feet and a million people live in slums, that is easier said than done.

From Mumbai to Rio de Janeiro to Johannesburg, the same story is playing out in some of the world’s most unequal regions, where tens of millions live in crowded slums without adequate water, sanitation and access to health care.

“The future of this pandemic to a greater extent will be determined by what happens in very large and densely populated countries,” Dr. Michael J. Ryan, executive director of the World Health Organization’s health emergencies program, said this week.

Experts believe the virus is mainly spread through droplets expelled from the mouths and noses of infected people when they speak, cough or sneeze, traveling 3 to 6 feet before gravity pulls them to the ground. And while most people suffer mild or moderate symptoms like cough or fever, in older adults and people with other health problems, the risk of pneumonia or death is far higher.

Social distancing, while necessary in the face of such an easily spread virus, envisions a “citizen who is able to live in the most desirable way,” said Hyun Bang Shin, a professor of urban studies at the London School of Economics and Political Science. “Injustices and inequities that have basically been embedded are being exposed in face of this outbreak.”

In Mumbai — where the city and its suburbs have seen a tenth of India’s nearly 900 cases — 53-year-old Abrar Salmani lives with 11 family members in a house so small that many regularly sleep outdoors in the Bhim Nagar slum.

The unemployed weaver said most families don’t have access to water and rely on communal washrooms for bathing.

In the Gaza Strip, where 2 million Palestinians live squeezed into 140 square miles and more than half are unemployed, the arrival of the virus this week prompted the territory’s Hamas rulers to order the closure of cafes and wedding halls and to cancel Friday prayers at mosques. Residents were urged to stay at home and refrain from close contact.

Across Africa, home to some of the world’s fastest-growing cities with badly strained infrastructure, authorities worry the virus could swiftly spread through slums and impoverished townships.

Tear gas and gunfire have been used in a couple of cities in a rough bid to enforce social distancing. So far the continent of more than 1.3 billion people has nearly 3,500 cases, but with the global shortage of testing kits, the actual number could be higher, and health experts have warned the rising rate looks like that of Europe.

In South Africa’s crowded, impoverished townships, tens of thousands of workers pack into groaning minibus taxis for commutes with little or no protection. At home, extended families squeeze into a single room or two and communities draw water from collective taps. A countrywide began Friday.

“Coronavirus scares us since we’re living [so close] in a shack,” said one Soweto resident.