The US death toll from Covid-19 surpassed 600,000 on Tuesday, although officials hailed progress towards a return to normality as its world-leading vaccination program promised to turn the page on one of the worst health crises in American history.

The United States has racked up by far the largest national death toll -- ahead of Brazil and India -- after a heavily-criticised early response to the pandemic, but has since organised among the world's most effective immunization drives.

Progress against the coronavirus was underlined as New York announced more than 70 percent of adults had received at least one vaccine dose and the last of the state's restrictions could be lifted.

"There's still too many lives being lost," President Joe Biden said, noting that despite the daily number of dead dropping sharply, the continuing loss of life was still "a real tragedy."

"My heart goes out to all those who have lost a loved one," he said, speaking on Monday in Brussels as the Johns Hopkins University tally ticked close to 600,000.

Biden has set July 4 as the target date for 70 percent of US adults to have received at least one dose, but several states in the South are lagging far behind and the country might miss that goal.

In New York city -- where more than 33,000 died from Covid -- life took a major step forward as almost all restrictions were lifted.

"We have hit 70 percent vaccination," Governor Andrew Cuomo said.

"It is the national goal, and we hit it ahead of schedule. What does 70 percent mean? It means that we can now return to life as we know it."

'REOPENING DAY'

California -- the first US state to enact a stay-at-home order just under 15 months ago -- also celebrated its "reopening day" Tuesday by lifting almost all pandemic-related social distancing and capacity limits.

Vaccinated people will be free to ditch their masks in nearly all of the nation's richest and most populous state, though exceptions will remain for locations including public transport, schools and hospitals, reports AFP.

"Finally we are here, June 15, to turn the page, to move beyond capacity limits... move beyond social distancing and physical distancing," Governor Gavin Newsom said at a ceremony to mark "the full reopening of the California economy."

"We saw way more death than we'd ever like to see -- we held way too many hands because families were not able to come into the unit," said nurse Helen Cordova, the first Californian to get a vaccine dose last December.

The capital Washington entered the 70 percent club on Monday.

The EU yesterday agreed to lift coronavirus restrictions for US travellers as Western countries moved toward a return to pre-Covid life, but in a stark reminder that the global pandemic was far from over, Moscow ordered mandatory jabs over a "dramatic" rise in infections.

Whether the US vaccination program succeeds in ending America's chapter of the pandemic will depend on authorities' ability to reach vaccine holdouts, who remain the most vulnerable to the coronavirus. Experts are particularly worried about the rise of the Delta variant, first identified in India.

VACCINE DOSING GAP

India's main opposition party, Congress, yesterday questioned the decision by Prime Minister Narendra Modi's government to double the gap between the doses of the AstraZeneca Covid-19 vaccine, asking whether it was prompted by a vaccine shortage.

On Tuesday, Reuters reported that the government had increased the gap without the agreement of the scientific group that it said recommended the move, citing three members of the National Technical Advisory Group on Immunisation (NTAGI) advisory body.

Congress leaders, including former party president Rahul Gandhi, said the government was trying to cover up a vaccine shortage.

"India needs quick & complete vaccination," Gandhi said in a tweet.

The government yesterday defended its decision to double the gap between the two doses of the AstraZeneca vaccine to up to 16 weeks.

It said the NTAGI's working group on May 10 initially recommended increasing the dosing interval to 12-16 weeks, a proposal that was subsequently taken up by a larger NTAGI committee on May 13.

"We have a very open and transparent system where decisions are taken on scientific basis," said N K Arora, chairman of the working group, according to a second government statement yesterday.

Meanwhile, a 34-year-old Covid-19 survivor was diagnosed with green fungus (Aspergillosis) infection in central Indian state Madhya Pradesh's Indore city in possibly the first case of this type of virus in the country.

India has so far reported black and white fungus among those who were either afflicted by Covid-19 or were recovering from the virus, reports our New Delhi correspondent.

Ravi Dosi, head of the Department of Chest Diseases at Sri Aurobindo Institute of Medical Sciences (SAIMS), said the man, who had recovered from Covid-19, underwent a test on suspicion that he had contracted the dreaded black fungus infection (mucormycosis).

But he was instead found to have green fungus (Aspergillosis) infection in his sinuses, lungs and blood, Dosi said.