India on Monday overtook Brazil as the country with the second-highest number of coronavirus infections and Bangladesh halted international flights and shut offices as a new wave battered South Asia.
The region -- home to almost a quarter of the world's population -- has been hit by soaring infection rates in recent weeks.
India reported a new daily record of more than 168,000 cases on Monday to take the total toll to 13.5 million cases, above Brazil's 13.48 million.
Experts have blamed coronavirus complacency and frustration for the surge.
Hundreds of thousands of maskless Hindu devotees thronged the banks of the Ganges River for a ritual bath as part of the Kumbh Mela festival in the holy city of Haridwar.
The huge religious festivals and political rallies in poll-bound states have been widely accused as cases grow among the population of 1.3 billion.
In neighbouring Bangladesh there was a mad scramble for buses and trains after the government ordered an eight-day closure of all offices and international and domestic transport from Wednesday.
Tens of thousands of people flocked to Dhaka's main bus, train and ferry stations to flee the capital ahead of the shutdown.
The country of 160 million people has recorded 684,756 cases and 9,739 deaths, but the number of daily cases has increased sevenfold in a month.
Hospitals across the nation say they are being overwhelmed by the new cases, and daily deaths have more than doubled.
"There is no alternative now to this in order to curb the Covid-19 surge," junior minister Farhad Hossain said ahead of the clampdown announcement.
Indian authorities have also warned of tougher restrictions unless the public keeps to social distancing and the wearing of masks.
"The whole country has been complacent -- we allowed social, religious and political congregations," Rajib Dasgupta, a health professor at Jawaharlal Nehru University in Delhi, told AFP.
India has recorded more than 873,000 cases in the last seven days -- an increase of 70 percent compared to the previous week, according to data compiled by AFP.
In comparison, Brazil recorded about 497,000, about 10 percent higher from the previous week.
The United States -- the worst-hit country -- reported just under 490,000 cases with a rising trend of nine percent.
The spike in India, after daily rises in cases fell below 9,000 in early February, has seen many badly affected states and territories impose restrictions on movement and activities.
India's wealthiest state Maharashtra, which has been the main driver of the infection spike, last week imposed a weekend lockdown and night curfew.
But Maharashtra has warned that a complete lockdown -- a drastic measure that national and state governments have tried to avoid to protect the already devastated economy -- could be imposed within the next few days as cases continue to rise.
"The solution is for everyone to stay home for two months and end this (pandemic) once and for all. But the public doesn't listen," said Rohit, 28, a waiter at a popular Mumbai restaurant who moved to the financial hub for work from the northern state of Punjab.
"Nobody follows the rules in the restaurant... If we tell customers to wear masks, they are rude and disrespectful to us."
The chief minister in New Delhi, where a night curfew is in place, said Sunday that two thirds of new Covid-19 patients were younger than 45.
He said the government would consider imposing a lockdown if hospital beds start running out.
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