The number of people who had been in close contact with the first patient in China with Middle East respiratory syndrome rose to 77 in Guangdong, the provincial Health and Family Planning Commission said on Sunday.
Among them, 64 have been quarantined while 13 others, including 11 passengers on a bus to Huizhou boarded by the man, have remained out of contact.
None of the quarantined has showed any abnormality.
The condition of the first patient, a 44-year-old South Korean man, aggravates, but he is conscious, his vital signs are stable, and his heart rate and blood pressure normal.
He flew from Seoul to Hong Kong on Tuesday, a day after his father was diagnosed with MERS, and travelled to Huizhou by bus on the same day, ignoring instructions from doctors to stay home.
MERS is a respiratory tract illness caused by the MERS coronavirus.
The first known human case was confirmed in Saudi Arabia in 2012, and since then 1,142 cases in 23 countries had been reported up until May 16. There is no vaccine or treatment for the illness.
The current outbreak has been traced to a 68-year-old man diagnosed on May 20 after returning from a trip to Saudi Arabia.
Eighteen people in the Hong Kong Special Administrative Region who had close contact with the patient in Huizhou have been sent to a quarantine camp－including two South Korean women who had earlier been reported to have refused to be quarantined－the Hong Kong Department of Health's Center for Health Protection said on Sunday.
The top health authorities in Guangdong and Hong Kong have issued notices asking people who were onboard Asiana Airlines OZ723 and two buses with the patient to report to them immediately.
Central Hospital in Huizhou has trained 160 nurses for the disease. Guangzhou Daily reported that the nurses were selected by lot to work with the South Korean patient in the intensive care unit.
Lin Jianfeng, a director in charge of infectious disease prevention at the Guangdong Center for Disease Control and Prevention, said the possibility of widespread human-to-human infections is remote.
He said 158 people were on the same flight as the patient and 41 people were on the same buses with him. "The toughest job now is to track all of the passengers on the buses," he added.
The South Korean Health Ministry said the country had 15 patients infected with the virus as of Sunday.
Wang Xiaodong and Xinhua contributed to the story.
Related: ROK apologises for outbreak of MERS
South Korea's health minister apologised on Sunday for failing to halt an outbreak of the MERS virus, vowing the "utmost efforts" to halt the disease's spread as the number infected rose to 15.
"We apologise for causing concern and anxiety among people due to ... our initial judgment on the contagiousness of MERS," Minister Moon Hyung-pyo said.
Moon added that this week would be a "critical period" to contain the spread of MERS, or Middle East respiratory syndrome, which can cause symptoms ranging from flulike aches and pains to pneumonia and kidney failure.
Health officials have come under fire for allowing an infected man to travel to China despite warnings from doctors.
The 44-year-old left on a business trip on Tuesday, a day after his father was diagnosed with the virus, and he was confirmed Friday to have been infected himself.
The man flew to Hong Kong and travelled by bus to Huizhou, Guangdong province, where he is being treated under quarantine.
Dozens of people - including his colleagues and passengers who sat near him on the same flight - have been or are expected to be examined or quarantined.
The outbreak has been traced to a 68-year-old man diagnosed on May 20 after returning from a trip to Saudi Arabia.
The 14 others who caught the virus were patients in the same hospital as the man, their relatives or hospital workers he came into contact with.
Moon said the hospital where the outbreak was reported has been closed and all patients were being treated in quarantine - he would not disclose its name or location for fear of spreading panic.
MERS is considered deadlier but less infectious than the related severe acute respiratory syndrome, which killed hundreds of people when it appeared in Asia in 2003.
A total of 129 people who were exposed directly or indirectly to the patients have been quarantined or put under special observation so far.
But "a far greater number" will be quarantined or put under observation this week as more people were diagnosed with the disease over the weekend, health officials said.
More than 20 countries have been affected by the virus with no known cure or vaccine, with most cases were in Saudi Arabia, where more than 400 have died since 2012.