Nearly a billion Indians stayed indoors on Sunday, heeding Prime Minister Narendra Modi's appeal to citizens to self-isolate as authorities battle to contain the fast-spreading coronavirus pandemic.

At least 324 people so far have contracted the disease while four have died in India, according to official data.

While the lockdown is voluntary and not an outright ban on the movement of people, Modi's appeal for social distancing has helped dramatically reduce the number of people taking to India's densely crowded streets.

Modi asked India's 1.3 billion people to stay home on Sunday and collectively cheer for front-line healthcare workers at 5pm local time (11:30 GMT).

Shortly before 5pm, the cacophony in capital New Delhi began as people on balconies and rooftops clapped, rang bells, banged on pots and pans, played music recordings and set off fireworks, sending crows and parakeets streaming from treetops, and stray dogs and cows into the deserted streets.