South Korea confirmed five MERS cases Friday, bringing the total number of patients infected with the potentially deadly virus to 12, including a man who defied a quarantine protocol and travelled to China, health officials said.

The infections were all traced to the original case of a 68-year-old man diagnosed on May 20 after returning from a trip to Saudi Arabia.

Middle East Respiratory Syndrome (MERS) is considered a deadlier but less infectious cousin of the Severe Acute Respiratory Syndrome (SARS) virus that appeared in Asia in 2003 and killed hundreds of people, mostly in China.

Symptoms may range from flu-like aches and pains to pneumonia and kidney failure.

The health ministry said the new MERS cases included a 30-year-old nurse from the hospital where the original case was reported, and a 56-year-old man who was treated there for other diseases.

A 44-year-old man who left for China on a business trip on Tuesday, a day after his father was diagnosed with the virus, was confirmed Friday to have been infected, it said.

The man ignored a warning from doctors advising against travel and is now at a hospital in China. A list of 45 people, including colleagues and passengers who had sat close to him on the Hong Kong-bound flight, has been drawn up.

The man later travelled from Hong Kong to the nearby Chinese city of Huizhou by bus.

Hong Kong's health authorities said they had tracked down and would quarantine 12 people -- three Korean, nine Chinese -- who had close contact with the man on the flight and were still in the city.

"They will be sent to our quarantine camp later this evening," the Hong Kong's Centre for Health Protection chief Leung Ting-hung told reporters.

Leung added that two other passengers on the plane, not part of the group of 12, had shown mild respiratory symptoms and were being examined at a Hong Kong hospital.

South Korea's second largest flag carrier, Asiana Airlines, remains on alert as the man used one of its flights, Yonhap news agency said, adding six crew members had been put in isolation.

Health officials said more than 120 people were being monitored after they were exposed directly or indirectly to the original patient.

More than 20 countries have been affected by the virus, with most cases in Saudi Arabia where more than 400 have been killed since 2012.

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