According to the US-based firm, India's online population will touch 283.8 million by 2016, leaving behind the US at 264.9 million in the same period.

EMarketer predicts that by 2018 India will have 346.3 million Internet users against the US' 274.1 million.

China, which has the world's largest Net users, will continue to retain its position with a little over 700 million by 2016 and 777 million by 2018, it added.

"Inexpensive mobile phones and mobile broadband connections are driving Internet access and usage in countries where fixed Internet has been out of reach for consumers, whether that's due to lack of infrastructure or affordability," eMarketer Senior Forecasting Analyst Monica Peart said.

While highly developed markets are nearly saturated in terms of Internet users, there is a significant room for growth in emerging ones, she said, adding that India and Indonesia will both see double-digit growth in each year between now and 2018.

"By 2016, India will jump the US as the second-largest Internet user population," eMarketer said.

Globally, Internet users will surpass 3 billion in 2015, increasing by 6.2% to reach 42.4% of the entire world's population, it added.

This year, the Internet will reach more than two in five people in the world for the first time as online audience hits 2.89 billion users globally, it said.

By 2018, eMarketer estimates that nearly half the world's population, 3.6 billion people, will access the Internet at least once each month.

However, a report by Internet and Mobile Association of India (IAMAI) and IMRB International predicts that India will overtake the US as the second-largest Internet user base in the world by December 2014.

The number of Internet users in India is expected to grow 32% to 302 million this year from 213 million at the end of December last year, it has said.

According to IAMAI-IMRB report, presently China leads with more than 600 million Internet users, while the US has an estimated 279 million users.