By Aditya Kalra and Zeba Siddiqui

NEW DELHI/MUMBAI (Reuters) - Drug retailers shut up shop for the day on Wednesday to protest against the country's growing online pharmacy industry, and threatened to close indefinitely if the federal government did not shut down e-pharmacies.

The nationwide protest was widely supported, with as many as 850,000 chemists closing their doors, leaving patients waiting in long queues at any pharmacies that were open.

"I have been to 7-8 shops that were closed. My son has fever, and he needs medicine urgently," said Sukanti Bhoi, 55, as she waited for her turn at a government hospital pharmacy in Odisha.

Shops inside and around hospitals as well as 24-hour pharmacies did not join in the one-day strike.

Online pharmacies are a relatively new phenomenon in India, where mom-and-pop stores have long dispensed drugs. But online retailers pose a threat to their bricks-and-mortar peers in a market IMS Health estimates is worth about $13 billion.

Companies including Zigy and Sequoia Capital-backed 1mg have set up e-pharmacies over the past couple of years. Healthcare company Apollo Hospitals Enterprise (APLH.NS) plans to start online sales if the government regulates the business.

Drug retailers are worried.

"It is a matter of our livelihoods, we must be prepared for a fight," said pharmacist Satish Vij, who travelled from northern Haryana to take part in a protest in New Delhi, where about 1,000 people, mostly pharmacists, wore black arm bands, held placards and shouted slogans against e-pharmacies.

"We will struggle if multinationals enter this business," he said.

J.S. Shinde, president of the All India Organization of Chemists and Druggists which called the protest, said the retailers' trade group will consider an indefinite strike if the government does not stop online drug sales within two months.

The dispute pits drug retailers, many of whom belong to the middle-class voter-base of Prime Minister Narendra Modi's Bharatiya Janata Party, against the leader's push to encourage tech and digital entrepreneurship in India.

Late on Tuesday, in a last-minute attempt to get pharmacies to stay open, Modi's Health Ministry said it was studying several representations on how the online pharmacy business should be regulated. It said the views of all stakeholders will be considered.

A Health Ministry spokeswoman could not immediately be reached for comment on Wednesday.

But retailers do not even want the government to consider online pharmacies as a legitimate business. They say online sales will lead to more cases of drug abuse as medicines will be sold without proper verification.

E-pharmacies say they have safeguards in place. Prashant Tandon, president of the newly formed group of e-pharmacies -- Indian Internet Pharmacy Association -- said the internet will also help small drug stores grow faster.

(Additional reporting by Jatindra Dash in Bhubaneswar; Editing by Paritosh Bansal and Adrian Croft)