A lockdown was reimposed on 15 million people in southern India on Friday as the number of coronavirus infections in the hard-hit nation neared 400,000. 

New restrictions in Chennai, the capital of Tamil Nadu state, and surrounding districts followed a surge of cases, even as the rest of the country of 1.3 billion people gradually resumes normal life. 

During the 12-day lockdown, food shops and petrol stations will be allowed to open between 6:00 am and 2:00 pm.

People can only travel within two kilometres (1.2 miles) of their homes except for medical emergencies.

"If someone calls me for air conditioner servicing then I will walk over if it is within a two-kilometre radius," said Kumar, the owner of an electrical repair shop in Chennai where normally bustling streets were quiet.

"But I heard that the cops are going to be really strict about movement on the streets after 2:00 pm."

India has recorded more than 380,000 cases of COVID-19, the fourth-highest in the world, with over 12,500 deaths, health ministry data show.  

Many experts say limited testing means the real figures are likely much higher. 

This week India hiked its official death toll by more than 2,000 after financial hub Mumbai increased the number of fatalities by almost 900 following an audit of its data.

The virus is raging across South Asia, home to some of the most crowded and poorest cities in the world, overwhelming hospitals and crematoria. 

Meanwhile, Indian Prime Minister Narendra Modi has extolled yoga as a way of building a "protective shield" of immunity against the coronavirus, as his nation battles a surge in infections.

Modi, a keen yoga practitioner who has long espoused the benefits of the ancient Indian practice, gave the advice in a YouTube message ahead of World Yoga Day on Sunday.

"We all know that until now nowhere in the world have they been able to develop a vaccine for COVID-19 or coronavirus," Modi said in the video published Thursday.

"Which is why right now, only a strong immunity can act as a protective shield or a bodyguard for us and our family members... yoga is our trusted friend in building this protective shield (of immunity)."

The Indian leader, a teetotal vegetarian, set up a ministry to promote yoga, Ayurveda and other traditional Indian treatments when he came to power in 2014.

Modi initially proposed World Yoga Day to the United Nations, winning approval in 2014. 

The day normally see masses of people gather for public yoga events not only in India but worldwide but Modi called for people to this year "go indoors".  

Modi also hailed yoga as a way to ease the extraordinary stresses people are enduring because of the virus.

"Yoga has the potential to cater to the mental, physical and psychological challenges. It puts to test how one can live in challenging times," he said.

In January, the Ministry of AYUSH (Ayurveda, Yoga & Naturopathy, Unani, Siddha, Sowa Rigpa and Homoeopathy) released an advisory on how ancient homoeopathy and Ayurveda remedies could help Indians combat the coronavirus.

But experts, including the US' National Institutes of Health, have warned that "no scientific evidence that any of these alternative remedies can prevent or cure COVID-19".