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

The positive news from America -- 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 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 since emerging in China in December 2019.

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 (CDC) on Sunday.

The US is a world leader in vaccinations, but a recent surge in new daily infections prompted top pandemic advisor Anthony Fauci to warn Sunday 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.

But Fauci predicted the J&J jab would soon return to circulation, albeit possibly with some restrictions or warnings on its use.