South Korean rescue members carry a woman in front of a public notice on Mers at the National Medical Centre in Seoul on Monday.

AFP/Seoul

South Korean President Park Geun-Hye scolded health officials on Monday over their "insufficient" response to an outbreak of the Mers virus, as the number of infections climbed to 18, with nearly 700 under observation.

There have been no deaths since the first case was reported on May 20 - one elderly patient is described as in a serious condition - but the emergence of the virus has triggered widespread public alarm.

Middle East Respiratory Syndrome (Mers) is considered a deadlier but less infectious cousin of Severe Acute Respiratory Syndrome (Sars), which killed hundreds of people when it appeared in Asia in 2003.

"The initial response to Mers... was insufficient," Park told a meeting of aides, calling for "all-out" government efforts to curb any further spread.

The president's comment came a day after health minister Moon Hyung-Pyo apologised for underestimating the initial threat of the virus.

The health ministry said on Monday that a total of 682 people who were exposed directly or indirectly to the virus have now been quarantined or put under special observation.

Health officials were particularly criticised for allowing an infected man to travel to China last week 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 was confirmed on Friday to have been infected himself.

The current outbreak has been traced to a 68-year-old man diagnosed after returning from a trip to Saudi Arabia.

The 17 others who acquired the virus were patients in the same hospital as the man, their relatives or hospital staff with whom he came into contact.

So far there has been no case of tertiary infection.

More than 20 countries have been affected by the virus, which has no known cure or vaccine, with most cases in Saudi Arabia where it has claimed more than 400 lives since 2012.

The South Korean outbreak is the largest among countries outside the Middle East.

Total of 77 people had contact with Mers patient: China

China is searching for 13 people who came into contact with the first person to enter the country with the Mers virus, health officials said, adding that 64 had already been quarantined.

Eleven people who travelled on a bus with a 44-year-old man from South Korea who entered China with the disease are among the 13 that are being sought, health officials in the southern province of Guangdong said.

The man flew to Hong Kong from Seoul on Tuesday last week, before later travelling overland to Huizhou in Guangdong by bus, ignoring the advice of doctors to stay at home, the China Daily newspaper said on Monday.

He is currently under quarantine, where "his vital signs are stable, and his heart rate and blood pressure normal", it added.