The total number of MERS virus infections in South Korea has risen to seven, officials say.

South Korean officials say they have confirmed two more MERS virus infections, bringing the total number of cases to seven, as one suspected victim ignored warnings and flew to China on a business trip.

The infections, all traced to the original case of a 68-year-old man diagnosed on May 20 after returning from a trip to Saudi Arabia, have triggered public concerns of a wider outbreak.

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 Korea Centre for Disease Control and Prevention said more than 70 people who may have been exposed directly or indirectly to the original patient were currently in voluntary quarantine.

However, one of them, a 44-year-old man, left for China on a business trip on Tuesday, a day after his father was diagnosed with the virus.

"We advised him against the trip but he refused," CDC director Yang Byung-Guk told reporters.

Yang said the Chinese health authorities had been notified and the man had been admitted to a Chinese hospital for testing following his arrival.

A list of 28 passengers who had sat close to the man on the China-bound flight had also been drawn up, he added.

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