Middle East Respiratory Syndrome (Mers) has risen to the top of the list of risks facing the aviation industry, the head of a leading aircraft lessor said, outstripping traditional concerns about fuel and currencies.

An outbreak of Mers in South Korea that began last month and is the largest outside Saudi Arabia has infected 166 people, killing 24 of them.

"You see airlines cancelling some flights out of Taiwan, out of China, to Korea, and tour groups beginning to cancel. So we hope we get over this quickly and that the world has learned from Sars, but the jury's out," Robert Martin, chief executive of Singapore-based leasing firm BOC Aviation, told Reuters.

Shares of Thai aviation firms and hoteliers fell on Friday after Thailand confirmed its first case of Mers.

The Thai case may compound fears in Asia of a repeat of a 2002-2003 outbreak of Severe Acute Respiratory Syndrome (Sars), which began in China and killed about 800 people worldwide.

"This has become the number one risk over the last few weeks. The problem with Mers is that it's harder to catch, but the fatality rate is higher once you've got it," Martin said in an interview.

"It's the fact that people then say to their families ... I really don't want you to travel to Korea. It's the fear factor. This is why we need it to blow over quickly."

Mers was first identified in humans in Saudi Arabia in 2012 and the majority of cases have been in the Middle East. Isolated cases cropped up in Asia before South Korea's outbreak and Thailand is the fourth Asian country to register a case.

Moody's Investors Service warned on Thursday that Mers could hurt South Korea's economic recovery as the Health Ministry reported three new cases, though there were also signs the outbreak is slowing.

The International Air Transport Association estimates that Asia-Pacific airlines lost about 8 per cent of their annual traffic due to Sars, costing them $6 billion in lost revenues.

According to the Geneva-based group that represents more than 250 airlines, while Sars caused relatively few deaths worldwide, a loss of confidence can ripple through travel and tourism, imposing heavy economic damage.

Martin said, however, that the Sars outbreak also showed confidence tends to return quickly once such shocks evaporate. – Reuters