The US has become the first country to record more than 2,000 deaths from coronavirus in a single day, as its overall toll surpassed that of Italy, making it the worst-hit country in the world.

White House experts said there were some signs the spread of the disease may be levelling off, but the US now has more than half a million confirmed infections and in the last 24 hours 2,108 people died. Hotspots include New York, Detroit, Louisiana and the capital, Washington DC.

By Saturday afternoon, Johns Hopkins University’s tally so far of US Covid-19 fatalities was at 18,860. Italy followed with 18,849.

It is unclear how long the US’s patchwork lockdown will need to stay in place, and the federal government has been at odds with regional politicians about everything from supplies of medical equipment to testing and lockdown exit strategies.

“No matter how long I live, I don’t think I will ever get over how the US, with all its wealth and technological capability and academic prowess, sleepwalked into the disaster that is unfolding,” Kai Kupferschmidt, a German science writer, told the Associated Press.

In Spain there was some hope after a third consecutive fall in the daily death toll that the country may now be reaching the so-called “stabilisation phase”.

Although the prime minister, Pedro Sánchez, suggested another month of movement controls were likely, from next week some non-essential workers will be allowed to start returning to their jobs, for example, in factories and construction sites. Masks will be handed out to travellers on public transport.

With infections worldwide now over 1.7 million and still climbing fast, however, few governments are expecting a rapid return to normal. Italy and India were among several other countries announcing official extensions to their lockdown periods, although Delhi did not say how long the new controls would last.

Italians will now be expected to stay home until at least 3 May. With discontent about the long shutdown growing, the interior ministry issued a warning on Saturday about the risk that extremist groups may try to take advantage of the crisis to foment violence.

The interior minister, Luciana Lamorgese, asked the police to intensify checks owing to “serious tensions” and the risk of “riots by groups of extremists”. The mafia have also used the crisis to bolster support by distributing free food to poor families in quarantine, authorities said.

There is growing consensus worldwide that the only way out of lockdowns – until a vaccine is found – is through a combination of testing, contact tracing and tight controls. South Korea is one potential model: at one point it was the worst-hit country outside China, but it has run an extremely successful suppression campaign.

However, it announced that because some of the 57,000 people who have been ordered to stay at home as part of quarantine efforts had been slipping out, it would be issuing tracking wristbands to those who defy orders. At present it is using phones to monitor movement, but people have evaded those checks by simply leaving their devices at home.

In a worrying development, South Korean officials on Friday reported that 91 patients thought to be clear of the coronavirus had tested positive again. Jeong Eun-kyeong, the director of the Korea Centers for Disease Control and Prevention, told a briefing that the virus may have been “reactivated” rather than the patients being re-infected.

The World Health Organization said it was looking into the reports. “We are closely liaising with our clinical experts and working hard to get more information on those individual cases. It is important to make sure that when samples are collected for testing on suspected patients, procedures are followed properly,” it said.

There are also concerns about the spread of coronavirus in Africa after the continent passed the grim milestones of 10,000 confirmed cases and more than 500 deaths, the BBC reported. A shortage of testing capacity in many countries has led to concerns that the spread of the disease may be hard to trace.

Despite efforts to lock down cities and countries, and despite donations of protective equipment, testing kits and ventilators from China, it is clear Africa has not yet flattened the curve and the room for manoeuvre is getting smaller.

Meanwhile, in war-divided Cyprus the coronavirus crisis may have offered an unexpected boost to reunification efforts. Officials said the president of the island’s internationally recognised Greek south, Nicos Anastasiades, had agreed to send vital medicines and other materials to the breakaway Turkish-run north after holding talks with the state’s leader, Mustafa Akıncı.

In China, the government reported three deaths and 46 additional cases in the 24 hours to midnight on Friday. The number of new daily cases has declined dramatically, allowing the ruling Communist party to reopen factories and stores. China has reported 3,339 deaths and 81,953 confirmed infections, though critics said the real totals might be higher.