Alarm over an outbreak of Middle-East Respiratory Syndrome (MERS) in South Korea spread on Thursday with North Korea calling for border checks while hundreds of schools closed in the South as authorities reported five new cases.
South Korean President Park Geun-hye has demanded that everything to be done to halt the outbreak which began two weeks ago, after a South Korean man returned from a business trip to the Middle East.
Two people have subsequently died in South Korea. With 35 cases, South Korea has the most infections outside the Middle East where the disease first appeared in 2012, and where most of the 440 fatalities have been.
About 1,600 people have been quarantined in South Korea, most of them at home or in medical institutions, a health ministry official said.
Among the five new South Korean cases were two more health workers who were treating infected patients.
"We are in a war," said an official at a health centre in Seoul's wealthy Gangnam district, where panic spread early on Thursday when medical workers in protection suits were spotted near a hotel.
The official said a Middle-Eastern guest at the hotel fell ill and was later confined in quarantine at a hospital.
"I saw some people dressed in scary white spacesuits on the street," said a 30-year-old woman resident of Gangnam.
MERS infection is caused by a coronavirus from the same family as the one that caused SARS, or Severe Acute Respiratory Syndrome, which emerged in 2002-2003 and killed around 800 people worldwide.
MERS has a much higher death rate - 38 percent, according to WHO figures - but also spreads far less swiftly than SARS from person to person, making it less of a threat for now.
North Korea had asked the South to provide heat-detecting cameras to monitor temperatures of workers travelling to the inter-Korean Kaesong Industrial Complex, just north of the border, a South Korean government official said.
South Korea lent North Korea three cameras to use at the complex during the recent scare over Ebola, the official said. South Korean authorities have been criticised for being slow to respond to the initial spread of MERS.
It took several days for the 68-year-old man returning from the Middle East to be diagnosed with MERS and in the meantime, he infected people at health facilities where he went for treatment for a fever and cough.
All of South Korea's cases have been traced to the man who visited Saudi Arabia and the United Arab Emirates, the countries with the most MERS cases.
China last week reported its first case, that of a South Korean man who tested positive after breaking a voluntary house quarantine and travelling to Hong Kong and on to mainland China.
More than 700 schools in South Korea were closed or had classes cancelled as of Thursday, the Ministry of Education said.
While there has been no sustained human-to-human transmission, the worst-case scenario would be for the virus to change and spread rapidly.
South Korea's new cases bring the total number globally to about 1,180, based on World Health Organization (WHO) data, with at least 442 related deaths.