The global tourism industry has been devastated by the coronavirus pandemic, with $320bn lost in exports in the first five months of the year and more than 120 million jobs at risk, the United Nations chief has said.

In a policy briefing and video address on Tuesday, Secretary-General Antonio Guterres said international tourist arrivals decreased by more than half because of the global health crisis, which has crippled the world's economies.

Tourism is the third-largest export sector of the global economy, behind fuels and chemicals, and it employs one in every 10 people worldwide, Guterres said. In 2019, it accounted for 7 percent of global trade.

"That is why it has been so painful to see how tourism has been devastated by the COVID-19 pandemic," the UN chief said.

The coronavirus pandemic has killed more 813,000 people worldwide amid more than 23.6 million cases, according to data collected by the Johns Hopkins University. Nearly 15.3 million have so far recovered.

In an attempt to curb the spread of the virus, countries around the world have taken sweeping measures, including full lockdowns, shutting down airports, imposing travel restrictions and completely sealing their borders.

Guterres said the crisis has been a "major shock" for wealthier developed nations "but for developing countries, it is an emergency, particularly for many small island developing states and African countries."

Tourism for some countries represents more than 20 percent of their gross domestic product (GDP), according to the UN.

Sandra Carvao, the UN World Tourism Organization's chief of market intelligence and competitiveness, said the $320bn in lost exports from January through May is three times what was lost during 2009 at the height of the last global financial crisis.

And according to the policy briefing, "export revenues from tourism could fall by $910bn to $1.2 trillion in 2020" and that "could reduce global GDP by 1.5 percent to 2.8 percent."

In addition to tourism jobs that are at risk, the policy paper said jobs in associated sectors, including food service, that provide employment for 144 million workers worldwide are also at risk.

It stressed that small businesses "are particularly vulnerable".

Guterres said tourism "is also a key pillar for the conservation of natural and cultural heritage."

"The fall in revenues has led to increased poaching and habitat destruction in and around protected areas," the secretary-general said, "and the closure of many World Heritage sites has deprived communities of vital livelihoods."

Guterres called for the tourism sector to be rebuilt in a way that is safe for host communities, workers and travellers, and is also "equitable and climate friendly".

He urged countries to mitigate the socioeconomic effects, maximise the use of technology and promote sustainability and green growth to aid recovery.

Noting that travel restrictions and border closures still remain though some have been lifted, Carvao said: "The recovery will be very much dependent on the evolution of the pandemic and the economic situation."

"No country has escaped the impact of COVID-19 on tourism," she said.