Leaders of the 20 biggest economies on Saturday vowed to ensure a fair distribution of Covid-19 vaccines, drugs and tests around the world and do what was needed to support poorer countries struggling to recover from the coronavirus pandemic.

"We will spare no effort to ensure their affordable and equitable access for all people, consistent with members' commitments to incentivize innovation," the leaders said in a draft G20 communique seen by Reuters. "We recognise the role of extensive immunization as a global public good."

The twin crises of the pandemic and an uneven, uncertain global recovery dominated the first day of a two-day summit under the chairmanship of Saudi Arabia, which hands off the rotating presidency of the G20 to Italy next month.

The Covid-19 pandemic, which has thrown the global economy into a deep recession this year, and efforts needed to underpin an economic rebound in 2021, were at the top of the agenda.

"We must work to create the conditions for affordable and equitable access to these tools for all peoples," Saudi Arabia's King Salman bin Abdulaziz said in his opening remarks. G20 leaders are concerned that the pandemic might further deepen global divisions between the rich and the poor.

"We need to avoid at all costs a scenario of a two-speed world where only the richer can protect themselves against the virus and restart normal lives," French President Emmanuel Macron told the summit.

To do that, the European Union urged G20 leaders quickly to put more money into a global project for vaccines, tests and therapeutics - called Access to Covid-19 Tools (ACT) Accelerator - and its COVAX facility to distribute vaccines.

"At the G20 Summit I called for $4.5 billion to be invested in ACT Accelerator by the end of 2020, for procurement & delivery of COVID-19 tests, treatments and vaccines everywhere," European Commission head Ursula von der Leyen said on Twitter.

"We need to show global solidarity," she said. Germany was contributing more than 500 million euros ($592.65 million) to the effort, Chancellor Angela Merkel told the G20, urging other countries to do their part, according to a text of her remarks.

Russian President Vladimir Putin offered to provide Russia's Sputnik V coronavirus vaccine to other countries and said Moscow was also preparing a second and third vaccine. China, where the pandemic originated a year ago, also offered to cooperate on vaccines. China has five home-grown candidates for a vaccine undergoing the last phase of trials.

"China is willing to strengthen cooperation with other countries in the research and development, production, and distribution of vaccines," President Xi Jinping told the G20 Summit.

"We will ... offer help and support to other developing countries, and work hard to make vaccines a public good that citizens of all countries can use and can afford," he said.

U.S. President Donald Trump, who lost the U.S. presidential election but has refused to concede to former Vice President Joe Biden, addressed G20 leaders briefly before going golfing. He discussed the need to work together to restore economic growth, White House Press Secretary Kayleigh McEnany said in a summary released late on Saturday. She made no mention of any U.S. pledge to support the global vaccine distribution effort.

One European source said Trump's remarks were focused on what he described as an unprecedented U.S. recovery and the U.S. drive to develop its own vaccines.

To prepare for future outbreaks, the EU is proposing a treaty on pandemics. "An international treaty would help us respond more quickly and in a more coordinated manner," European Council President Charles Michel told the G20.

While the global economy is recovering from the depths of the crisis, momentum is slowing in countries with resurgent infection rates and the pandemic is likely to leave deep scars, the International Monetary Fund said in a report for the summit.

Especially vulnerable are poor and highly indebted countries, which are "on the precipice of financial ruin and escalating poverty, hunger and untold suffering", United Nations Secretary-General Antonio Guterres said on Friday.

To address this, the G20 will endorse a plan to extend a freeze in debt service payments by the poorest countries to mid-2021 and endorse a common approach for dealing with debt problems beyond that, the draft communique said.

World Bank President David Malpass warned the G20 that failing to provide more permanent debt relief to some countries now could lead to increased poverty and a repeat of the disorderly defaults of the 1980s.

The G20 debt relief initiative has helped 46 countries defer $5.7 billion in debt service payments, but that is far short of the 73 countries that were eligible, and promised savings of around $12 billion. Private sector participation is seen as critical to ensuring broader use of the initiative. Debt relief for Africa will be an important theme of the Italian presidency of the G20 in 2021.