Former British Prime Minister Gordon Brown accuses rich countries of committing a "moral outrage" by stockpiling COVID-19 doses while poor countries are suffering to get supplies.

Brown, who is a United Nations special envoy, called on US President Joe Biden and G7 leaders to urgently send part of the millions of vaccines stockpiled in their warehouses to Africa.

Western countries have a supply of nearly 300 million shots, while only 70 million people in Africa, the second-most populous continent, have so far been vaccinated, Brown said citing research by data firm Airfinity.

By Christmas, the West is set to have 1 billion surplus doses even if every European and American adult has received a booster shot and all children over 12 are injected, Ex-UK PM Brown said.

"We are in a new 'arms' race - to get vaccines into people as quickly as possible - but this is an arms race where the West has a stranglehold on the vaccine supplies," he said.

As the rich countries continue to tighten their grip on vaccine stocks, Covax, the international facility for buying vaccines, is facing a huge difficulty in keeping its promise of providing poorer countries with 2 billion vaccines this year, he added.

The stockpiling has also delayed dose-sharing by G7 countries with Africa and low-income countries, Brown said in an opinion piece published in the Sunday Mirror newspaper.