A top world health official has warned that countries are essentially driving blind in reopening their economies without setting up strong contact tracing to beat back flare-ups of the coronavirus.

The warning came as France and Belgium emerged from lockdowns, the Netherlands sent children back to school, and a number of US states continued to lift their business restrictions.

Fears of infection spikes in places that have loosened up have been borne out in recent days in Germany, where new clusters were linked to three slaughterhouses; in Wuhan, the Chinese city where the crisis started; and in South Korea, where one nightclub customer was linked to 85 new cases.

Authorities have warned that the scourge could come back with a vengeance without widespread testing and tracing of infected people’s contacts.

The World Health Organization’s emergencies chief, Dr Michael Ryan, said that robust contact tracing measures adopted by Germany and South Korea provide hope that those countries can detect and stop virus clusters before they get out of control.