Health authorities in Hong Kong on Friday were scrambling to trace some 200 fellow passengers of a Korean national believed to be infected with the Middle East Respiratory Syndrome (MERS) virus who landed in the former British colony earlier this week aboard an Asiana Airlines jet.
The 44-year-old man became China's first suspected case of MERS, which causes a severe respiratory illness with a 40 percent mortality rate, and for which there is no vaccine or treatment.
China's National Health and Family Planning Commission said the man arrived in China for a business trip on Tuesday.
"He has family members who are infected and had close contact with them back in Korea," the official Xinhua news agency quoted the ministry as saying.
The man began running a fever on Monday and landed in Hong Kong on Tuesday, before traveling across the internal immigration border to neighboring Guangdong province by cross-border bus, it said.
Chinese health authorities are now holding the man under observation in an isolation ward, and notified the World Health Organization on Wednesday, the report said.
Hong Kong is on high alert for the virus, which is in the same family of coronaviruses such as the SARS virus, which killed 299 people in the city in 2003.
The city's Centre for Health Protection said it is now tracing people who may have come into contact with the man, including 158 passengers on board the Asiana flight.
"Among them, 80 were in the same cabin, including 29 who were sitting within two rows of the MERS patient," the center said in a statement on the official government website.
Twelve people have already been sent to a quarantine camp for a two-week observation period, while around 10 are known to have left Hong Kong, the statement quoted center chief Leung Ting-hung as saying.
The center will also be looking for other passengers on the flight and cross-border bus service, with a view to placing them under medical surveillance, Leung told reporters.
Hong Kong's health chief Ko Wing-man said the authorities have set up a hotline to enable anyone who had contact with the man to come forward.
"I am very concerned about the outbreak of MERS because the transmission (of the disease) has never been stopped since it occurred more than two years ago," Ko said. "Reports of sporadic cases and clusters of cases continue."
Ko said Hong Kong's alert level has remained high since the emergence of MERS in Saudi Arabia in 2012.
"The most important thing for us now is to concentrate our efforts to search out the passengers on the same flight who have been identified as close contacts," Ko said.
U.S.-based medical doctor Jin Fusheng said the mainland Chinese health authorities would be making similar efforts to track down the patient's contacts.
"The relevant departments in Guangdong still need to find and place under observation every single person who has had contact with this person," Jin said.
He said it was lucky that the man had informed the Chinese authorities when he did.
"Some patients aren't public-spirited enough [to put themselves in quarantine], but at least the South Korean government informed the Chinese authorities," Jin said.
"Patients sometimes need to be told that the virus they have is infectious, and that they are being placed in quarantine and ...that they can't leave until they are fully recovered," he said.
He said MERS is a particularly deadly disease, compared with SARS.
"Doctors usually regard a 10 percent mortality rate as very high, so a mortality rate of [more than 40] percent is extremely high," Jin said.
He said the MERS virus, like SARS, is able to flourish in a variety of conditions.
"Depending on the climate, and other factors like the air, it can alter the proteins on its surface to mutate," Jin said, adding: "Generally, anyone showing symptoms must be held in isolation."
Procedures under scrutiny
China's public health procedures have come under intense scrutiny since an official attempt to cover up the extent of the deadly SARS epidemic of 2003 was exposed by a military doctor in Beijing.
The doctor was detained for several months in 2004 at an undisclosed location, while editors at a newspaper in the southern province of Guangdong that broke news about the SARS virus were also harassed and detained.
The outbreak of severe acute respiratory syndrome (SARS) spread from Guangdong to other Asian countries and by the summer of 2003, when the disease was contained, more than 8,000 people had been infected, and more than 900 had died, according to the World Health Organization.
Reported by Xi Wang for RFA's Mandarin Service and by Wen Yuqing for the Cantonese Service. Translated and written in English by Luisetta Mudie.