Past and present world leaders have urged that any eventual COVID-19 vaccines and treatments should be made available to everyone free of charge.

South African President Cyril Ramaphosa and Pakistani Prime Minister Imran Khan were among more than 140 signatories of a letter saying vaccine should not be patented while the science should be shared among nations.

The World Health Assembly (WHA), the policy-setting body of the World Health Organization, holds its annual general meeting next week.

The signatories called on the WHA to rally behind the cause.

"Governments and international partners must unite around a global guarantee which ensures that, when a safe and effective vaccine is developed, it is produced rapidly at scale and made available for all people, in all countries, free of charge," the letter said.

"The same applies for all treatments, diagnostics, and other technologies for COVID-19."

The letter was also signed by Senegalese President Macky Sall and Ghanaian President Nana Akufo-Addo.

Former presidents and prime ministers among the signatories included Shaukat Aziz, Jan Peter Balkenende, Jose Manuel Barroso, Gordon Brown, Helen Clark, Felipe Gonzalez, Ellen Johnson Sirleaf, Aleksander Kwasniewski, Mary McAleese, Olusegun Obasanjo and Juan Manuel Santos.

The letter comes amid fury in France after pharmaceutical giant Sanofi said it would reserve first shipments of any COVID-19 vaccine for the United States.

The French multinational company's chief executive Paul Hudson said the US would get first dibs because its government was helping to fund the vaccine research.

His comments drew outrage on Thursday from officials and health experts.

African Union Chairperson Ramaphosa said: "As the countries of Africa, we are resolute that the COVID-19 vaccine must be patent-free, rapidly made and distributed, and free for all.

"Nobody should be pushed to the back of the vaccine queue because of where they live or what they earn."