Visitors rush to the Mona Lisa as the Louvre re-opens

The world's most visited museum has projected an 80% plunge in visitor numbers as travel restrictions have only begun easing in Europe.

The sprawling former palace on the banks of the River Seine in Paris, home to works including Leonardo da Vinci's Mona Lisa and the Winged Victory of Samothrace, closed its doors in mid-March.

Customers are obliged to book tickets and safety measures are observed, including mandatory face masks and a one-way system through certain rooms.

The museum says time-specific slots will allow it to control numbers at peak period.

But 75 percent of visitors come from abroad and European borders with the top two countries of origin, the United States and China, remain closed, meaning the museum will remain comparatively empty in the summer season during which it normally sees a million visitors a month.

Museum director Jean-Luc Martinez said the lockdown had come at a cost: 40 million euros in lost ticket office revenue, cancelled events and shop sales.