The UN body said the full extent of the fall in international tourism would depend on how quickly international borders open again.

Under a best-case scenario, with travel restrictions starting to ease in early July, international tourist arrivals could fall by just 58 percent.

If borders and travel restrictions are only lifted in early December, the fall would be more in the order of 78 percent.

If the restrictions are lifted in early September, the UN body predicts a fall of 70 percent.

Under these scenarios, the drop in international travel could lead to a loss of $910 billion to $1.2 trillion in export revenues from tourism, and of 100 to 120 million direct tourism jobs.

The body had forecast at the beginning of the year that international tourism would grow by 3 to 4 percent in 2020, but then revised its forecast at the end of March, predicting a 20 to 30 percent decline.

International tourism arrivals rose by 4 percent in 2019 to 1.5 billion, with France the world's most visited nation, followed by Spain and the US.

The last time international tourist arrivals posted an annual decline was 2009 when the global economic crisis hit the travel sector hard.

The tourism industry accounts for about 10 percent of the world's gross domestic product and jobs.