G20 leaders said Sunday they will "spare no effort" to ensure the fair distribution of coronavirus vaccines worldwide, and support poor countries whose economies have been ravaged by the crisis.

As the pandemic rages, the club of the world's richest nations adopted a unified tone on the challenges ahead during a virtual summit hosted by Saudi Arabia.

But after a weekend of "digital diplomacy", their closing communique lacked details on many of the issues dominating the meeting.

"We have mobilised resources to address the immediate financing needs in global health to support the research, development, manufacturing and distribution of safe and effective Covid-19 diagnostics, therapeutics and vaccines," they said in the statement.

"We will spare no effort to ensure their affordable and equitable access for all people."

While richer nations plan their vaccination programmes, with the US expecting to launch in early December, experts warn that developing countries face hurdles that could deny billions the first proven protection against the virus.

Calls are mounting for the G20 to help plug a $4.5-billion funding gap in the so-called ACT-Accelerator, a mechanism led by the World Health Organization that aims to ensure access to tests, treatments and vaccines for all.

In a comment echoed by other world leaders, French President Emmanuel Macron said Saturday that the coronavirus crisis was "a test for the G20", stressing there "will be no effective response to the pandemic unless it is a global response".

However, the final statement did not spell out how the massive cost of the exercise would be underwritten.