TOKYO -- Half of the new undersea communication cables to be built over the next three years will connect to Asia as Google, Facebook and other big-name tech companies look to harness the region's mushrooming demand for bandwidth.

Google is participating in four deep-sea cable projects, such as one linking Guam with China. Those hookups are expected to come online as early as next year. Google says the maps, videos and other services it provides hinge on infrastructure that is both fast and reliable. Late last year, Facebook and Amazon joined Japan's NTT Communications and SoftBank Group to fund a 14,000km project connecting the U.S., Japan and the Philippines. Once it goes live in early 2020, the cable will be able to deliver 60 terabits of data a second. Microsoft is also backing underwater cable projects.

The entry of internet heavyweights in a domain normally reserved for telecommunications companies is driving the rapid expansion of Asian deep-sea networks. Over the three years through 2020, builders will lay about 137,000km of cable serving 18 Asian nations and jurisdictions, data from U.S. research firm Telegeography shows. That represents a 33% jump from the approximately 103,000km installed over the three years through 2017.

The construction is fueled by expectations of a steep rise in regional internet demand ahead of the launch of 5G wireless services and the ongoing spread of "internet of things" technology. Monthly data volume in the Asia-Pacific region will rise to 108 quintillion bytes in the year 2021, according to U.S. technology group Cisco Systems. The estimate is up roughly 2.5 times from last year, and enough to fill more than 25 billion DVDs.

When it comes to cables linking Asia with the U.S. mainland, four projects are slated between 2018 and 2020, or twice the number in the three years through 2017.

Undersea networks are also adding capacity between Asia and Oceania. Australian telecom group Telstra is participating in multiple deep-sea cable projects, including the 4,600km Indigo connection between the continent and Singapore. An improved cross-border network means that customers will be able to find business opportunities in growth markets more quickly and easily, said Paul Abfalter, Telstra's director for emerging markets.

In Indonesia, a nation of thousands of islands, a public-private partnership has been set up to construct undersea and terrestrial cables. The 36,000km Palapa Ring fiber optic network -- divided into three sections -- will be built until it covers the country's entire 5,000km span. The goal is to develop e-commerce and other digital-based domestic businesses.

Nikkei staff writers Jun Suzuki in Jakarta and Fumi Matsumoto in Sydney contributed to this story.