World leaders are to hold online crisis talks Thursday on the coronavirus pandemic that has forced three billion people into lockdown and claimed more than 21,000 lives.

With the disease tearing around the globe at a terrifying pace, warnings are multiplying over its economic consequences, and experts are saying it could cause more damage than the Great Depression.

Amid squabbling between the leaders of China and the US over who is to blame, UN Secretary General Antonio Guterres called for the world to act together to halt the menace.

"COVID-19 is threatening the whole of humanity -- and the whole of humanity must fight back," Guterres said, launching an appeal for $2 billion to help the world's poor.

"Global action and solidarity are crucial," he said. "Individual country responses are not going to be enough."
The global lockdown -- which rolled through India's huge population this week -- tightened further Thursday as Russia announced it was grounding all international flights.

Economists say the restrictions imposed around the world to fight the virus could cause the most violent recession in recent history.

"The G20 economies will experience an unprecedented shock in the first half of this year and will contract in 2020 as a whole," rating agency Moody's said.