A bird's eye view of commercial and residential buildings stand as seen from a skyscraper during construction development in Central Jakarta.

Southeast Asia's internet economy is predicted to exceed $240 billion by 2025 as affordable mobile internet drives rapid growth in sectors such as e-commerce and ride-hailing, according to a new study released by Google and Singapore's Temasek Holdings on Monday.

That's $40 billion more than a previous estimate the companies made in 2016. The study focused on six Southeast Asian countries — Singapore, Indonesia, Malaysia, Vietnam, Thailand and the Philippines — across four main areas: ride-hailing, e-commerce, online media and online travel. Within those areas, the report added new sectors such as online food delivery, music subscriptions and video on demand.

By the end of 2018, the region's internet economy is predicted to be about $72 billion, up 37 percent from a year earlier, as measured by gross merchandise value — a key industry metric measuring total dollar value of merchandise sold online.

Indonesia has the largest and fastest-growing internet economy in Southeast Asia, and is predicted to grow to $100 billion by 2025 and account for 40 percent of the region's spending, according to the report.

Affordable mobile data and improvements in connectivity has led to more internet users in Southeast Asia; more than 90 percent of them are accessing the world wide web through their smartphones, the report said. The six countries studied in the report have around 350 million internet users today compared to only 260 million in 2015, making Southeast Asia among the fastest growing internet regions in the world.

"We're adding about 3 million net new internet users every single month. They're accessing the internet almost entirely through a mobile device," Rajan Anandan, vice president for India and Southeast Asia at Google, told CNBC's "Squawk Box" on Monday.

He explained that for the average user in Southeast Asia, their first point of connection to the world wide web is through mobile internet — unlike in the West, where people mostly first connected to the internet through fixed connections from their homes, likely on their desktops.

In recent years, mobile internet has also become more affordable as the price per gigabyte of data has dropped by nearly 50 percent over the last two to three years, according to Anandan.