Delhi's coronavirus doubling rate at 15 days is more than double of Mumbai's at 39 days.
The total number of coronavirus cases in Delhi has crossed the 70,000-mark, displacing Mumbai as the worst hit-city in India which recorded 16,922 new patients - the biggest day-on-day surge for a second consecutive day.
Delhi is also the second worst-hit state in terms of coronavirus caseload and fatalities after Maharashtra.
According to official figures, the COVID-19 numbers in Delhi soared by 3,788 to touch 70,390, though Mumbai was not far behind with a total of 69,528 cases.
Experts have said that density of population is a huge factor in spread of COVID-19 and it must be noted that Delhi's total area is more than double of Mumbai's.
The city-state's coronavirus doubling rate is also 15 days - more than double of Mumbai's at 39 days.
The rising number of COVID-19 cases has forced the governments of both the states to rethink their containment strategy, which now comprises use of a combination of tests to check spread clusters and symptomatic patients.
The Delhi government plans to screen all homes in containment zones by June 30; it plans to attain this target for the entire city by July 6.
Mumbai's BMC also aims to test every citizen for COVID-19.
For this, the municipal body has launched Mission Universal Testing, and has decided to buy 1 lakh antigen test kits which will make Covid-19 testing easier. The civic body will make antigen kits available at all civic and state-run hospitals. Private hospitals have also been advised to buy these kits.
Meanwhile, the country's top medical body adviced the Central government to "make testing widely available as it still remains a huge challenge in a large country like India".
As the pandemic claimed 14,894 lives, with 418 succumbing in the past 24 hours, the Indian Council of Medical Research said all hospitals, offices and public sector units should be allowed to conduct antibody-based COVID-19 testing to help allay fear among workers.
The situation has also forced some states to impose partial lockdowns in containment zones.
At the same time, the recovery rate has steadily improved to reach 56.71 per cent, the data showed.