A woman (right) hugs a family member before her departure to New Zealand at Sydney International Airport on Monday, as Australia and New Zealand opened a trans-Tasman quarantine-free travel bubble. Photo: AFP

The hard-hit United States has passed a hopeful milestone as half its adults have had at least one COVID-19 vaccine dose and from Monday all its over 18s will be eligible to get their shot.

The positive news from the US, the world's hardest-hit country, comes amid easing restrictions for several European nations and the launch of a quarantine-free travel bubble between Australia and New Zealand. 

But in India, authorities were scrambling to free up hospital beds and secure additional supplies of oxygen and treatment drugs as the vast nation reported a record daily caseload.

More than a quarter of a million new infections were tallied on Sunday, with health workers bracing for further surges as millions of pilgrims attend a religious festival and ongoing state elections draw huge rallies.

The coronavirus has killed more than 3 million people and infected at least 140 million, devastating the world economy and upending daily life.

Roughly 130 million Americans aged 18 and over have now received a shot, representing 50.4 percent of the adult population, according to the Centers for Disease Control and Prevention.

The US is a world leader in ­vaccinations, but a recent surge in new daily infections prompted top pandemic advisor Anthony Fauci to warn that the country remains in a "precarious position."­

White House efforts to speed up vaccinations hit a snag when health authorities reported six cases of young women developing a clotting disorder after taking the Johnson & Johnson shot. 

Australia and New Zealand got a glimpse of normal life on Monday, as a long-awaited quarantine-free travel ­bubble opened across the Tasman Sea.

Family members tearfully reunited at Sydney's airport, while others readied for their first outbound flights in more than a year after New Zealand closed its doors in response to the pandemic.

The opening received saturation coverage from media in both countries, with live television reporting from airports providing regular updates on the progress of flights.