India's three most affected cities - Mumbai, Delhi and Chennai - between them account for a growing share of India's new Covid-19 cases each day, to the point that as of June 1, they accounted for 44 per cent of all cases in India. But which of them is getting better, and which is in trouble?

The data for this piece comes from "covid19india.org", Mumbai and Chennai's municipal corporation Twitter handles and the official coronavirus websites of New York City, Russia and Brazil.

While the pandemic in India has been concentrated among its biggest cities so far, it's these three cities that are in the most difficult position at the moment. While Mumbai has more cases and deaths than the other two put together, Chennai's burden of cases proportionate to its population is higher than that of Delhi.

Over the last two weeks, the three most affected cities have begun to converge in terms of new cases discovered every day. Chennai's new cases are growing fast, and beginning to show signs of outstripping even Delhi, which has twice as many people.

Until the last week of April, cases were growing fastest in Mumbai, but first Chennai and now Delhi have faster daily growth rates than Mumbai. Mumbai is testing far too little for its caseload, with just three times as many cases as tests. Delhi too should test more given its rate of discovery, while Chennai's daily testing data is not available.

India's worst affected cities are now inching towards the worst affected cities of the world - New York City, Sao Paulo and Moscow - in terms of new cases each day.