Some 2.9 billion people -- 37 percent of the world's population -- have still never used the internet, the United Nations said Tuesday, despite the Covid-19 pandemic driving people online.

The UN's International Telecommunication Union estimated that 96 percent of those 2.9 billion live in developing countries.

The agency said the estimated number of people who have gone online rose from 4.1 billion in 2019 to 4.9 billion this year, partially due to a "Covid connectivity boost".

But even among those internet users, many hundreds of millions might only go online infrequently, using shared devices or facing connection speeds that hamper their internet use.

"ITU will work to make sure the building blocks are in place to connect the remaining 2.9 billion. We are determined to ensure no one will be left behind," said ITU secretary-general Houlin Zhao.

The number of users globally grew by more than 10 percent in the first year of the Covid crisis -- by far the largest annual increase in a decade.

The ITU cited measures such as lockdowns, school closures and the need to access services like remote banking.

But the growth has been uneven. Internet access is often unaffordable in poorer nations -- almost three-quarters of people have never been online in the 46 least-developed countries.

Younger people, men and urbanites are more likely to use the internet than older adults, women and those in rural areas, with the gender gap more pronounced in developing nations.

Poverty, illiteracy, limited electricity access and a lack of digital skills continue to challenge the "digitally excluded", the ITU added.