(Bloomberg) — Amazon opened its largest campus building globally in the south Indian city of Hyderabad as it prepares for a furious expansion and battle with nemesis Walmart in one of the world’s fastest-growing retail markets.

The Seattle-headquartered company is making an ambitious push in India, the last major retail frontier still primarily reliant on small-scale neighborhood and mom-and-pop stores. “E-commerce is so small in India relative to the total consumption, less than 3%,” said Amit Agarwal, Amazon’s country manager for India.

The largely untapped country is critical to the global domination plans of both Amazon and Walmart, the latter of which spent $16 billion last year to buy India’s biggest startup, retailer Flipkart Online Services. Amazon founder Jeff Bezos has so far pledged $5.5 billion for its India operations.

Built in Hyderabad over three years, the new campus is Amazon’s first owned building outside of the United States, spans 1.8 million square feet of office space, or about 50 times the footprint of the Taj Mahal’s mausoleum.

It will accommodate 15,000 workers. “The largest buildings in Seattle house about 5,000 employees,” remarked John Schoettler, vice president of Amazon’s Global Real Estate and Facilities. He said the campus was Amazon’s largest in the world but has plenty more room to grow.

“This facility will build services globally,” Agarwal added, citing examples like AWS, Kindle, Alexa, Amazon.in and Amazon Home Services, which is “innovating on things like doorstep pick-up and electronics repair.”

At the same time as it’s inaugurating its new Indian hub, Amazon is investing on other fronts within the nation. It is in negotiations to buy a 10% stake in one of India’s largest brick & mortar retailers, Future Retail, people familiar with the matter have said.

Local media have also reported that Amazon is eager to add food delivery to its Indian repertoire and is negotiating with multiple food companies to kick-start that line of business.

Amazon started its retail operations in India in 2013 and has since added several services to boost sales, including an expansion into producing Bollywood originals to boost its Prime Video loyalty program in the movie-loving country. Prime membership in India has doubled over the past 18 months, according to Agarwal, and he still sees “tremendous growth” going forward.