Incheon International Airport (Photo/ Xinhua)

GUANGZHOU, May 31 -- Authorities in south China's Guangdong Province are still trying to reach 13 people who had close contact with the country's first Middle East Respiratory Syndrome (MERS) patient.

A man from the Republic of Korea (ROK) was tested positive for the deadly MERS in Guangdong on Friday. He is receiving medical treatment in Huizhou City with doctors saying his situation has worsened, the provincial health and family planning commission said Sunday.

Meanwhile, the number of people who had been in close contact with the patient rose to 77 in Guangdong, the commission said. Among them, 64 have been quarantined while 13 others, including 11 passengers on a bus boarded by the man, have remained out of contact.

None of the quarantined has showed any abnormality.

The commission said more medical specialists were sent to Huizhou on Sunday to help with the treatment.

The man, 44, flew from the ROK to Hong Kong on Tuesday and entered Huizhou City via Shenzhen. He had close contact with MERS patients at home and expressed discomfort as early as May 21.

The patient is the son of the third confirmed MERS case in the ROK and the brother of the ROK's fourth confirmed case.

MERS is a respiratory illness caused by a new type of corona virus. The first case was identified in Saudi Arabia in 2012. There is no vaccine or treatment for the disease, which has a fatality rate of 40.7 percent.