NEW DELHI • One recent Wednesday afternoon, monsoon rains were lashing office windows in Mumbai. Inside, screens were lighting up with messages announcing the arrival of Cyclone Phyan.
Employees of a start-up called Little Black Book, an online city guide, started panicking. Some went home early after receiving messages on their phones that roads were being closed.
Others passed the message on to loved ones in Phyan's path.
Ms Jayati Bhola, a 24-year-old writer at Little Black Book, was organising a charity music show that evening and feared that the warning may put off her guests. She quickly checked the weather online and then sent around a message: "We're still on guys! Rain or Shine."
As it turns out, Cyclone Phyan never came to Mumbai that evening of Sept 20. In fact, it had already happened - eight years earlier, 2,250km away, in Sri Lanka.
"That rumour about the cyclone has been going around for years," said Mr Pankaj Jain, founder of SMXHoaxSlayer.com, a website that fact-checks rumours circulating on social media in India.
While fake news in the United States is said to have helped Mr Donald Trump become President, in India, which has 355 million Internet users, false news stories are part of daily life, exacerbating weather crises, increasing violence between castes and religions, and even affecting public health matters.
"Common sense is extinct," Mr Jain said. "People are ready to believe anything."
Last week, newspapers in New Delhi carried full-page advertisements by Facebook that explained how to spot false news.
Much of India's false news is spread through WhatsApp. One message that made the rounds last November, just after the government announced an overhaul of the country's cash, claimed that a newly released 2,000 rupee bank note would contain a GPS-tracking nano-chip that could locate bank notes hidden up to 118m underground.
That same month, a rumour about salt shortages prompted a rush on salt in four Indian states.
And a rumour about a measles and rubella vaccine thwarted a government immunisation drive.
In May, rumours about child abductors in a village triggered several lynchings and the deaths of seven people.
Some stories exacerbate India's rising religious and caste tensions. Recently, images purportedly showing attacks against Hindus by "Rohingya Islamic terrorists" in Myanmar circulated on India's social media, stoking hatred in the Hindu-majority country against the Muslim Rohingya.
The rumours have resulted in a small industry of fact-checkers who are setting up websites to debunk myths circulating online.
Former software engineer Pratik Sinha, who started Altnews.in, a fact-checking website, said: "The number of fake news stories is so high that we can't compete on the quantity of fact checks we do... We focus on quality."
The scrutiny has led to some triumphs. Ministers have deleted misleading tweets and posts after being fact-checked online.
Mr Jain said the rise of false rumours worries him. "Somebody's making money out of all this," he said, saying that clicks on fake news websites are supported by advertisements. "Ultimately, people are being conned."