BRUSSELS — New coronavirus clusters have surfaced around the world as nations struggle to balance reopening economies and preventing a second wave of infections, while a top global health official warned Wednesday that COVID-19 could be around for a long time.

Authorities in the Chinese city of Wuhan, where the pandemic first began late last year, reportedly were pressing ahead Wednesday to test all 11 million residents for the virus within 10 days after a handful of new infections were found.

In Lebanon, authorities reinstated a nationwide lockdown for four days beginning Wednesday night after a spike in reported infections and complaints from officials that social distancing rules were being ignored.

A top World Health Organization official, meanwhile, warned that it’s possible the new coronavirus may be here to stay.

“This virus may never go away,” Dr. Michael Ryan said in a press briefing Wednesday. Without a vaccine, he said it could take years for the global population to build up sufficient levels of immunity.

“I think it’s important to put this on the table,” he said. “This virus may become just another endemic virus in our communities,” he said, noting that other previously novel diseases like HIV have never disappeared, but that effective treatments have been developed.

Despite the risk that loosening restrictions could lead to infection spikes, European nations have been seeking to restart cross-border travel, particularly as the summer holiday season looms for countries whose economies rely on tourists flocking to their beaches, museums and historical sites.

The European Union unveiled a plan to help citizens across its 27 nations salvage their summer vacations after months of coronavirus lockdown and resurrect Europe’s badly battered tourism industry. The pandemic has prompted border closures across Europe and shut down the lifeline of cheap local flights.

The EU’s executive arm, the European Commission, laid out its advice for lifting ID checks at closed borders, helping to get airlines, ferries and buses running while ensuring the safety of passengers and crew, and preparing health measures for hotels.