The International Rescue Committee (IRC) said financial and humanitarian aid were needed to help slow the global spread of the virus.
It said “fragile countries” such as Afghanistan and Syria needed “urgent funding” to avoid a major outbreak, reports the BBC.
“There remains a small window of time to mount a robust response,” it warned.
There have been more than three million confirmed cases of Covid-19 worldwide with more than 200,000 deaths, according to Johns Hopkins University in the US.
The IRC’s report, which is based on models and data from the World Health Organization (WHO) and Imperial College London, estimated there could be between 500 million and one billion infections globally.