The risk of a second wave of COVID-19 infections big enough to require European lockdowns to be reimposed is moderate to high, EU health experts said on Friday and depends on the gradual easing of restrictions and how people stick to them.

A pandemic risk assessment by the European Centre for Disease Prevention and Control also predicted a moderate pick-up in infection rates in the coming weeks, although it said transmission has passed its peak in most European countries.

"The pandemic is not over," ECDC Director Andrea Ammon said in a statement accompanying the assessment.

She said that while there are decreasing trends of COVID-19 infections across Europe, efforts are still needed to limit the spread of the disease.

"It is important to comply with recommendations regarding physical distancing and maintain high standards of hand hygiene and respiratory etiquette," she said. "Everyone's contribution makes a difference."

The Stockholm-based ECDC monitors and advises on disease and public health in the European Union.

Its assessment found that stringent physical distancing measures imposed by many governments have reduced transmission.

It also noted that the enforced stay-at-home orders have been "highly disruptive to society, both economically and socially" and that many countries have now begun a full or partial reopening of shops and public spaces.

"At the present time, just before the summer holiday period, as member states relax limitations, there is a risk that people will not adhere firmly to the recommended measures still in place due to 'isolation fatigue,'" the ECDC warned.

It said the risk of COVID-19 incidence rising to a level that may require the re-introduction of stricter control measures is high if lockdown measures are phased out when there is still ongoing community transmission, and if no appropriate monitoring, testing and tracing systems are in place.

The risk would be moderate, however, if measures are phased out gradually, if the transmission has been reduced to sporadic levels and if disease test-and-track systems are in place.

World Health Organization Director General Tedros Adhanom Ghebreyesus told a ceremony in Geneva late on Thursday that "the threat of a resurgence remains very real ... Now is the time to be even more vigilant.

"We must also remember that although the situation is improving here in Europe, globally it's getting worse. We still have a road ahead, and we will continue to need global solidarity to defeat this pandemic fully," Tedros said.