India on Monday became the country with the third-highest coronavirus caseload in the world, as a group of scientists said there was now overwhelming evidence that the disease can be airborne and for far longer than originally thought.

The country reported over 24,200 confirmed cases in 24 hours, taking the total to nearly 700,000 on Monday, slightly more than Russia.

India's major cities including New Delhi and Mumbai are suffering the most, and critics say not enough tests are being conducted, meaning that many COVID-19 infections are likely to go undiagnosed.

The surge has forced authorities in India to convert hotels, wedding halls, a spiritual center and even railway coaches to help provide care to coronavirus patients.

Despite the climbing coronavirus cases, the Indian government has gradually lifted virus restrictions to help the battered economy.

Silent slums

Mumbai's Dharavi slum, believed to be Asia's largest slum, has been hailed as a success story in the battle against the coronavirus pandemic, bringing cases from a daily average of 100 in April to about 10 in July, say city officials, thanks to a strict lockdown.

But cash-starved slum dwellers and informal traders fear a long-term hit to their income, as about 150,000 migrant workers have left Dharavi, according to official estimates and small businesses face permanent closure.

"Many factories have exhausted their capital and there is still no idea when things will start improving ... The small factories of Dharavi do not have the capacity to suffer this scale of loss," said Babu Khan, president of the Dharavi Garment Association.

"These factories can't afford to stop work even for a week. It has been about four months now. About 80 percent of the factories here are still shut," he told Reuters.

Particularly at risk are informal traders – which according to Khan make up 70 percent of businesses in Dharavi, as they are not eligible for bank loans or government schemes to boost lockdown-hit industries.

Business owner Rais, 60, who makes brass belt buckles, said that "silence means everything is shut. I have closed my business for good ... I could not sustain it."

"I don't know what I will do next ... I have never seen Dharavi like this before," said Rais, who goes by one name.

Airborne threat

Around the world, governments are struggling to balance the need to reopen economies wrecked by weeks of lockdown measures against the risk of new infections as people return to normal life.

Amid the re-openings came a stern warning from experts who said governments must recognize that coronavirus can spread through the air far beyond the two meters, urged in social distancing guidelines.

In a letter published this week in the journal Clinical Infectious Diseases, two scientists from Australia and the U.S. wrote that studies have shown "beyond any reasonable doubt that viruses are released during exhalation, talking and coughing in microdroplets small enough to remain aloft in the air." That means people in certain indoor conditions could be at greater risk of being infected than was previously thought.

The letter was endorsed by 239 scientists from a variety of fields, and they have called for the World Health Organization and others to acknowledge that the coronavirus can spread in the air.

The scientists recommended new measures including installing high-grade air filters and preventing overcrowding in buildings and transport systems.

"Hand washing and social distancing are appropriate, but in our view, insufficient to provide protection from virus-carrying respiratory micro-droplets released into the air by infected people," they said.

However, Indian health experts had warned that it's "impossible" to stop the fast-spreading virus in slums where social distancing is difficult due to cramped housing and poor sanitation.

The problems were compounded by the fact that people are eager to get their life back to normal.

Reopening

Factories in Dharavi are posting messages on social media and phoning workers to ask them to return, promising to cover their food and accommodation. But as some migrant workers begin to return, officials are going to brace for the challenges ahead.

"People are keen to reopen their factories, keen to resume work and are interacting with each other," said Kiran Dighavkar, an assistant municipal commissioner overseeing measures to contain the coronavirus in the area. "Few factories have started reopening and some labourers are returning."

"We have to ensure the habits of distancing and sanitization continue ... and that is our next challenge. This is a dynamic disease," he added.

Slum dwellers, who have got used to the sound of vehicles, the clank of metals and the hum of hundreds of sewing machines in workshops, in the meantime, are ready for the lockdown silence to end.

Farhana Sarfaraz Sheikh, 29, who migrated to Mumbai 15 years ago and found accommodation, training and a computer operator job in Dharavi, said noise meant there was work going on.

"It shouldn't be this quiet. Life has to begin," she said.

As people are returning to normal, authorities have used drones, re-oriented traffic cameras, and heat maps to help enforce a lockdown in what is one of the most densely populated areas on earth, and led an aggressive tracing and testing campaign.

In addition to daily screening and isolation centers, private clinics are also enlisted for early diagnosis and treatment, ensuring fewer people needed beds.

The peak stage of COVID-19 pandemic in India may arrive around mid-November, during which there could be a shortage of isolation and ICU beds, and ventilators, according to India's apex medical research body, the Indian Council for Medical Research.

(With input from AFP and Reuters)