The US could become the new centre of the global coronavirus pandemic, according to the World Health Organization, which said case numbers were rising quickly there even asDonald Trump talked of reopening the country for business.

“We are now seeing a very large acceleration in cases in the US. So it does have that potential [to become the centre of the pandemic],” said Margaret Harris, a WHO spokeswoman.

Meanwhile in India, Narendra Modi ordered a 21-day lockdown of the whole country, the world’s second most populous, after researchers warned more than 1 million people could be infected by mid-May.

“The only way to save ourselves from coronavirus is if we don’t leave our homes; whatever happens, we stay at home,” said the prime minister, who was giving his second address in less than a week to try to rally India’s 1.3 billion people to support the drastic measures.

“Every district, every lane, every village will be under lockdown. If you can’t handle these 21 days, this country will go back 21 years,” he said.

“The only option is social distancing, to remain away from each other. There is no way out to escape from coronavirus besides this.” So far India has reported 482 cases and nine deaths, but there is concern about the potential for the pandemic to spread rapidly

Hopes that Italy’s extensive lockdown was bearing fruit, with drops in reported deaths in recent days, proved to be premature. The numbers have risen by 743 to 6,820, the head of the Civil Protection Agency said on Tuesday, ending two days of decline in fatalities. Deaths dropped from 793 on Saturday to 651 on Sunday and just over 600 on Monday.

Angelo Borrelli, the top coronavirus response official in Italy, had earlier started to sound optimistic.

“The measures we took two weeks ago are starting to have an effect,” Borrelli said in an interview with La Repubblica. He said more data over the next few days would help officials understand “if the growth curve is really flattening”.

But he noted that the real number of infections was probably 10 times higher than the official count. He also said the nation of 60 million was on course to overtake China’s total number of confirmed Covid-19 cases in a week.

In the US, 46,450 people have become infected and there have been 593 deaths, according to the latest data from Johns Hopkins University.

Confirmed cases of Covid-19 in the US

There have been 46,724 confirmed cases across the US so far. The true number of cases is likely to be significantly higher.

Trump acknowledged that crucial healthcare supplies to protect frontline staff treating sick patients were becoming difficult to obtain.

In an early morning tweet, he said: “The world market for face masks and ventilators is crazy. We are helping the states to get equipment, but it is not easy.”

But while more US governors were urging people to stay at home, Trump appeared to play down the crisis on Monday night.

The president said he was considering ways to restart the economy in the coming weeks and wanted to avoid the pandemic becoming “a long-lasting financial problem”. It would not last as long as three or four months, he said.

“Our country was not built to be shut down,” Trump said. “This is not a country that was built for this.”

Later he tweeted: “Our people want to return to work. They will practice Social Distancing and all else, and Seniors will be watched over protectively & lovingly. We can do two things together. THE CURE CANNOT BE WORSE (by far) THAN THE PROBLEM! Congress MUST ACT NOW. We will come back strong!”

Trump’s senior advisers referred to current government restrictions as a “15-day challenge” and pledged to revisit in a week’s time the need for sweeping measures to prevent the spread of the virus.

But senior Pentagon leaders warned on Tuesday that the US epidemic could continue for months. “I think we need to plan for this to be a few months long at least and we’re taking all precautionary measures to do that,” said the defense secretary, Mark Esper.

The chairman of the joint chiefs of staff, Gen Mark Milley, said that, judging from other countries’ experiences, it could go on into July. “If it does apply, you’re looking at probably late May, June, something in that range, could be as late as July,” Milley said.

In Spain, meanwhile, the numbers infected and tested rose from 33,089 to 39,673 on Tuesday, according to the health ministry, while the death toll rose from 2,182 to 2,696.

Health workers accounted for nearly 14% of Spain’s total reported cases as of Tuesday, up from 12% the previous day, according to data presented by the health emergency chief, Fernando Simon.