India added a record number of coronavirus cases Sunday, approaching Russia as the world's third-most infected nation as it opens a mass treatment centre in the capital to fight the pandemic.

The health ministry reported just under 25,000 cases and 613 deaths in 24 hours -- the biggest daily spike since the first case was detected in late January.

The sharp rise came as Delhi started treating patients at a spiritual centre converted into a sprawling isolation facility and hospital with 10,000 beds, many made of cardboard.

About the size of 20 football fields, the facility will treat mild symptomatic and asymptomatic cases.

State government officials fear the metropolis could record more than half-a-million cases by the end of the month.

India's surge took the total tally to more than 673,000 cases and 19,268 deaths, with the country on the cusp of surpassing badly-hit Russia.

A strict lockdown in place since late March has gradually been lifted, allowing most activities as the economy nose-dived amid the shutdown.

Schools, metro trains in cities, cinemas, gyms and swimming pools remain closed however and international flights are still grounded. 

Authorities have made wearing masks mandatory in public places, while large gatherings are banned and shops and other public establishments are required to implement social distancing.

The western state of Maharashtra, the worst-hit state and home to financial hub Mumbai, recorded over 7,000 new cases.

Southern Tamil Nadu state and the national capital New Delhi recorded more than 4,200 and 2,500 fresh cases respectively.

Mumbai, Delhi and Chennai, Tamil Nadu's capital, are the worst-affected cities.

The national government says it has tackled the virus well but critics allege India is conducting very few tests, leaving the true scale of the pandemic unknown.

Meanwhile, Iranian health authorities on Sunday announced 163 new deaths due to the COVID-19 disease, the country's highest official one-day toll since the outbreak began in February.

The previous record of 162 deaths was announced on Monday in the Islamic republic, which has been battling the Middle East's deadliest outbreak of the novel coronavirus. 

The new deaths bring the total toll in Iran to 11,571, health ministry spokeswoman Sima Sadat Lari said on state television.

"In the past 24 hours, 2,560 people have tested positive for coronavirus, bringing the total number of infections to 240,438," Lari added.

Official figures have shown a rising trajectory in fatalities and new confirmed cases since Iran reported a near-two month low in daily recorded infections in early May. 

The increase has prompted the government to make the wearing of masks mandatory in enclosed public spaces in an effort to combat the spread of the virus.