Facebook has unveiled an app to allow people around the world with mobile phones but no internet access to access online services for health, education and basic communications.

The internet.org app is being released first in Zambia. It is to be rolled out then in other countries where internet access is lacking or unaffordable, Facebook said.

The app allows people with Android-powered mobile phones to get free access to services including Wikipedia, Google Search, Facebook, AccuWeather and websites offering health and other services.

"Over 85% of the world's population lives in areas with existing cellular coverage, yet only about 30% of the total population accesses the internet," Facebook's Guy Rosen said in a blog post.

"Affordability and awareness are significant barriers to internet adoption for many and today we are introducing the internet.org app to make the internet accessible to more people by providing a set of free basic services."

Facebook Chief Executive Mark Zuckerberg said the app is part of "our effort to bring affordable internet access to everyone in the world".

"We believe that every person should have access to free basic internet services - tools for health, education, jobs and basic communication," Mr Zuckerberg said on his Facebook page.

"Over the past year we've been working with mobile operators around the world to deliver on this goal.

"We're starting to see this vision become a reality, and we've already helped three million people access the internet who had no access before."