His warning comes amid dire predictions about the possible economic impact of measures imposed to fight the virus.
The number of confirmed cases around the world is now nearing 860,000, with more than 42,000 deaths.
The death toll in the US is now more than 4,000 – higher than the declared number of fatalities in China, where the outbreak began late last year.
Johns Hopkins University said 865 people had died in the past 24 hours in the US and in all more than 189,000 people in the country had been infected.
Meanwhile, Spain, second only to Italy in the number of recorded fatalities, has seen 849 deaths in the last 24 hours – the highest number it has had in a single day.
In the UK, a total of 1,789 people have died – a rise of 381, officials say. Among the victims was a 13-year-old boy, King’s College Hospital Trust in London.