Dr Mike Ryan, the WHO’s head of emergencies, told a briefing on Monday that the world was “right in the middle of the first wave”.

He said because the disease was “still on the way up”, countries need to be aware that “the disease can jump up at any time”.

“We cannot make assumptions that just because the disease is on the way down now that it's going to keep going down," Dr Ryan said.

There would be a number of months to prepare for a second peak, he added.

The stark warning comes as countries around the world start to gradually ease lockdown restrictions, allowing shops to reopen and larger groups of people to gather.

Experts say that without a vaccine to give people immunity, infections could increase again when social-distancing measures are relaxed.

Dr Ryan said countries where cases are declining should be using this time to develop effective trace-and-test regimes to “ensure that we continue on a downwards trajectory and we don’t have an immediate second peak”.