India is flexing its maritime muscles in the Indian Ocean.

Since 2011, India’s naval voyages across the world’s third-largest ocean have grown in number by 300%, according to consultancy firm IHS Markit, bolstering the country’s presence in a key region where China has been making inroads.

China has increasingly deployed nuclear and conventional submarines in the Indian Ocean as it looks to assert its dominance as a regional superpower, and counter India’s growing influence, in South Asia.

The Indian Ocean is a prominent trade route as nearly 36 million barrels of oil are transported daily through its shipping lines. This is roughly about 40% of the world’s oil supply. The ocean also accounts for 40% of the global offshore oil production. For India, as much as 95% of its trade and 80% of crude oil imports take place through the Indian Ocean.

“Dominance in the Indian Ocean translates, in a way, to dominance in Asia, because of the primary maritime trade routes and energy trade,” Caron Natasha Tauro, south Asia analyst for security research firm IHS Jane, said in a statement. “This boosted competition between India, which sees the ocean as its backyard, and China, which has the potential to enlarge its influence with the One Belt, One Road project and the Maritime Silk Road initiative.”

The One Belt, One Road project involves setting up of road and rail routes, oil and natural gas pipelines, and other infrastructure projects—running through central Asia to as far as Venice—and the setting up of ports and sea infrastructure between south Asia and the northern Mediterranean Sea.

Since coming to power in 2014, Indian prime minister Narendra Modi has spent considerable time engaging with the Indian Ocean Littoral nations. Last year, for instance, he visited Seychelles, Sri Lanka, and Mauritius, with an eye on countering China’s growing influence in the region.

India and Japan have also been considering building a sea wall of “hydrophones”—microphones with sensors placed on the seabed—between southern India and the northern tip of Indonesia. The move was aimed at keeping a check on Chinese submarine movement.

The navies of India, Japan, and the US also held a joint drill in the Philippine sea in June this year, irking Beijing.

While China had cut back on the number of visits to the Indian Ocean last year, perhaps to focus on the muddled South China Sea waters, it firmed up patrolling this year. The Chinese navy’s redeployment reflects the country’s “commercial interests and possibly to build relations with states like Pakistan and Bangladesh,” IHS Markit reckoned.

In all, between 2011 and 2016, the various navies of the Indian Ocean region have also stepped up their procurement budgets from around $8.5 billion to $12 billion. During these years, the navies of India, China, Bangladesh, and Pakistan have also been investing in attack submarines, destroyers, frigates, and mine warfare vessels.

The Indian Navy currently has a fleet of 137 ships while the Chinese Navy boasts a fleet of 300 ships. But, India plans to add some 100 new warships, including two aircraft carriers and three nuclear-powered submarines, over the next 12 years, spending $61 billion.

The prize is obvious. “The Indian Ocean is re-emerging in strategic significance, not just due to the previous risk of piracy,” said Lee Willett, head of IHS Jane’s naval desk, “but also due to the world’s naval superpowers seeing the chance to fill a strategic void at sea in the region.” Add to this the “elegant decline” of the US, including from the Indian Ocean region, and the field is open for others to step in.