Guterres urged the G20 to funnel more funds to impoverished countries, including via debt relief, and boost their access to COVID-19 vaccinations. He added that the economic recovery from the pandemic was amplifying inequalities.
"This is immoral," he said.
He also called on rich economies to make good on a longstanding commitment to provide $100 billion a year to help the developing world tackle the growing threat posed by climate change.
"Unfortunately, the message to developing countries is essentially this, the cheque is in the mail. On all our climate goals, we have miles to go. And we must pick up the pace," Guterres said.
Many of the leaders coming to Rome, including US president Joe Biden, will fly immediately afterwards to Scotland for the United Nation's climate summit https://www.reuters.com/business/environment/sticking-points-un-climate-conference-2021-10-18, known as COP26, which is seen as vital to tackling the threat of rising temperatures.
Guterres said revised climate pledges from some G20 nations did not inspire confidence.
"Even if recent pledges were clear and credible, and there are serious questions about some of them, we are still careening towards climate catastrophe," he said.