Social media has emerged as a leading source of news among online users who increasingly access it on their smartphones, a thinktank said on Wednesday, warning that the embrace of free news was becoming a challenge for publishers of quality news.

More than half of online users get their news from Facebook and other social media platforms, refusing to pay for news and using ad-blocking, which hurts publishers' revenue, the Reuters Institute for the Study of Journalism (RISJ) said.

But although free news distributed through social platforms creates an opportunity to reach more readers, it also makes it more difficult for publishers to get recognised and connect with their audience, the RISJ said in its annual Digital News Report.

"These things are happening because of us," Rasmus Kleis Nielsen, Reuters Institute director of research, told the Thomson Reuters Foundation in a phone interview.

"We prefer news in the digital form because it's convenient but you get what you pay for. It takes money to do professional journalism."

Facebook is playing an increasingly significant role in the distribution of online news, with 44 per cent of people using it as their source of news, followed by 19 per cent of people using YouTube and 10 per cent using Twitter, the report said.

Nielsen said that in developing countries, where access to independent and reliable news was limited, there were even more people who relied on social media for news.

"Many people in Asian and African countries are using mobile phones to get their online news and in those regions social media is even more important as source of news," he said.

Thirty-six per cent of people preferred news to be selected for them by algorithms compared with 30 per cent who relied on editors or journalists, although some feared missing key information or challenging viewpoints, the report said.

For the first time social media has overtaken television as the main source of news for 18 to 24-year-olds, with 28 per cent of them citing social media as their main source of news compared with 24 per cent who said they watched news on television.

More than half of the respondents said they were using smartphones to access news, with highest levels in Sweden (69 per cent), Korea (66 per cent) and Switzerland (61 per cent), the study said.

In Britain and the United States the use of smartphones to access the news has for the first time overtaken computers and laptops.

The survey was carried out online in 26 countries in Europe, Asia, North America and South America. – Thomson Reuters Foundation