More than 700 schools in South Korea have been closed as a third person died from the Mers virus and the number of people infected rose to 35.
South Korean authorities have been criticised over their response to the outbreak after one infected person went to play golf and another flew to China.
More than 1,600 people have now been quarantined, according to officials.
The outbreak is the largest outside the Middle East, where the disease first appeared in Saudi Arabia in 2012.
Five more cases were confirmed on Thursday, the South Korean health ministry said, bringing the total number of known infections in the country to 35.
The latest victim died in hospital after contracting the virus from another patient in the same room.
About 160 of those quarantined have been isolated at state medical facilities but most have been instructed to stay at home and strictly limit contact with other people.
The outbreak in South Korea is still confined to those with a link to the initial sufferer, but authorities are struggling to contain growing public anxiety.
In Seoul the number of people wearing face masks on public transport and in crowded places has increased.
And the Korea Tourism Organisation said on Thursday that about 7,000 tourists – mostly from China and Taiwan – had cancelled planned group trips to South Korea.
“A mass cancellation of this scale is very unusual… and many travellers cited the Mers outbreak as the main reason,” a spokesman told the AFP news agency.
The first case in this outbreak – “patient zero” – was a 68-year-old man who was diagnosed after returning from a trip to Saudi Arabia. He is still in hospital.
Mers – which stands for Middle East Respiratory Syndrome – can cause fever, breathing problems, pneumonia and kidney failure.
Experts believe it is not very contagious. Tan Wenjie, director of the virus department at the National Institute for Viral Disease Control and Prevention, said Mers could only spread “via close contact in a confined space”.
“And no evidence proves that it can spread through air, so people need not to feel panic,” he added.
There have been 1,167 cases of Mers worldwide, of which 479 have resulted in death, according to the European Centre for Disease Prevention and Control.
Nurses at a hospital in China reportedly drew lots to determine who should treat the country’s first case of Mers.
The virus has a death rate of 27%, according to the World Health Organization.