Officials around the world reintroduced a raft of restrictions Monday - from beach closures to quarantine measures - to try to tamp down coronavirus hotspots as the official global death toll passed 650 000.

European countries trying to repair the economic damage caused by the earlier lockdowns struggled to balance keeping the lifeline of tourism open while guarding against new flare-ups of infection.

WHO says travel bans cannot be kept up indefinitely, and are also only useful when combined with a wide range of other measures to detect and break chains of transmission.

The world’s biggest COVID-19 vaccine study got under way on Monday with the first of 30,000 planned volunteers helping to test shots created by the US government along with Moderna Inc - one of several candidates in the final stretch of the global vaccine race.

Hong Kong has announced further restrictions in a bid to curb a surge in coronavirus cases, including a ban on gatherings of more than two people, a ban on restaurant dining and mandatory face masks outdoors.