A woman wearing a mask walks past an information banner on Mers at the entrance of Bamrasnaradura Infectious Diseases Institute at a hospital in Nonthaburi province, on the outskirts of Bangkok on Friday.

Reuters/Bangkok

Thai authorities took nearly four days to confirm the country's first case of Middle East Respiratory Syndrome (Mers), the health ministry said on Friday, a time lag likely to raise fears of a further spread of the deadly virus in Asia.

Thailand confirmed its first case of Mers on Thursday, a 75-year-old businessman from Oman, just as an outbreak in South Korea that began last month and has infected 166 people, and killed 24 of them, appeared to be levelling off.

The infected man arrived in the Thai capital, Bangkok, on Monday on an Oman Air flight for medical treatment for a heart ailment at a private hospital.

Public Health Minister Rajata Rajatanavin declined to identify the hospital and said the patient had been put in quarantine at an infectious diseases institute in Bangkok on Thursday.

"It took about four days to diagnose this case and two lab tests," Rajata told Reuters.

Authorities wanted to monitor all 106 people on board the man's flight, he said, though it was not clear how everyone could be traced.

Among those being monitored were the man's two sons, who were considered at high risk because of their proximity to their father. The two had been tested and results were due later on Friday, Rajata said.

Most of those under observation had been told to stay at home for 14 days.

Shares plunge

The Thai case will 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 globally.

Shares in Thai aviation companies and hotels fell on Friday with hotel operator Central Plaza Hotel plunging 6.6%. Airports operator Airports of Thailand dropped 4.2% to a more than three-week low.

Mers was first identified in humans in Saudi Arabia in 2012 and the majority of cases have been in the Middle East.

Isolated cases have cropped up in Asia before South Korea's outbreak began last month, and Thailand is the fourth Asian country to register a case.

China has had one case recently, that of a South Korean man who travelled to China via Hong Kong despite authorities suggesting he stay in voluntary quarantine at home.

Thailand was screening passengers from countries seen at risk of Mers and stepping up public information about the virus, another health official said.

The Middle East is an important source of tourists for Thailand with arrivals from the region up by nearly 50% in January, according to the tourism office.

Bangkok is also one of the region's main aviation hubs.