Spain passed the landmark figure of 500,000 coronavirus infections on Monday as India reopened some metro lines despite becoming the world's second most affected country.

Spain had largely gained control over its outbreak by imposing one of the world's toughest lockdowns, but infections have surged since the restrictions were fully removed at the end of June.

The country became the first in western Europe to hit the 500,000 mark -- albeit with a far lower death rate and many more asymptomatic cases than were recorded during its previous peak in late March and early April.

"The situation is much more favourable but we remain in an upwards phase," said health official Fernando Simon.

But the overall caseloads in European countries are dwarfed by India's 4.2 million confirmed infections.

Nevertheless, economic necessity pushed the South Asian nation to risk reopening transport lines on Monday -- metros began running again in the capital New Delhi after a five-month shutdown and 12 other cities also restarted subway services.

"For our lives to move on, we have to get out of our homes... so this is a good move by the government," on commuter Deepak Kumar on the Delhi subway told AFP.

Passengers are obliged to wear masks, keep their distance and undergo temperature checks.

- 'Like guinea pigs' -

India leapfrogged Brazil to become the world's second-hardest hit nation after the United States, with the virus having caused almost 890,000 deaths and more than 27 million infections worldwide.

As governments around the world have moved away from the idea of blanket lockdowns, countries in all continents have been experimenting with targeted measures to deal with infection spikes.

England fiddled with its overseas quarantine rules again on Monday, imposing restrictions on travellers from seven Greek islands popular with holidaymakers.

Morocco imposed a lockdown on Casablanca and shut schools on the day they were supposed to reopen after a surge in cases in the city.

Officials said the virus risked overwhelming the country if it was not controlled, but some parents were left fuming.

"They were on cloud nine over returning to school tomorrow," wrote one father on Twitter. "How do you explain this to a six-year-old and an eight-year-old?" 

In Spain, parental anger flowed in the other direction, with fears rising that schools were opening too soon with millions of pupils returning on Monday.

"Going back to school is being treated like an experiment, we're like guinea pigs," said Aroa Miranda, a 37-year-old mother-of-two.

France put seven more regions on a red list on Sunday after regularly recording daily infection rates of between 7,000 and 9,000 -- although the figure fell dramatically on Monday.

Israel announced a "nightly closure" of 40 cities and towns with the highest infection rates with Prime Minister Benjamin Netanyahu accepting the measures were not ideal but saying there was "no way to avoid them".