The United States has warned against travel to India, where authorities on Tuesday imposed tighter restrictions to combat an explosion of Covid-19 cases.
India has recorded more than three million new infections and 18,000 deaths this month, bringing its caseload to the world's second-highest, after the United States.
The updated US travel advisory comes after the State Department announced on Monday it would apply "do not travel" guidance to about 80 per cent of countries worldwide, citing the unprecedented risk posed by the pandemic.
"Even fully vaccinated travellers... should avoid all travel to India," the US Centers for Disease Control and Prevention said.
Singapore also boosted restrictions on arrivals from India Tuesday, adding a week to the previously required 14-day quarantine period.
These moves follow Britain's decision on Monday to add India to its "red list", and Hong Kong's ban on all flights from the country.
India has been struggling to rein in its raging outbreak, with hospitals running out of beds and the government forced to reimpose economically painful restrictions.
Its capital and worst-hit city New Delhi entered a week-long lockdown on Monday, with parks, cinemas and malls closed.
"Delhi's health system is at a tipping point," said chief minister Arvind Kejriwal, who on Tuesday went into self-isolation after his wife tested positive.
The lockdown announcement prompted tens of thousands of migrant workers to flee Delhi, in scenes reminiscent of the national shutdown a year ago that inflicted economic and human misery.
Mumbai's home state of Maharashtra, the epicentre of the recent surge, on Tuesday further tightened restrictions on grocery shops and home deliveries.
All non-essential shops and malls in the western state are currently shut until May 1.
Uttar Pradesh, home to some 240 million people, on Tuesday announced a weekend lockdown from Friday evening, whilst Telangana state in the south became the latest to impose a night curfew.
Former Indian prime minister Manmohan Singh, 88, was admitted to hospital with the virus on Monday. Officials said Tuesday that his condition was stable.