South Korea's tally of patients of Middle East Respiratory Syndrome (MERS) rose to seven on Thursday, with authorities saying one suspected victim skipped out of voluntary home quarantine to take a trip to China. 

A rise in MERS cases has stirred alarm in South Korea, with health authorities being criticized for not moving quickly and effectively enough to quarantine suspected patients.

Two new victims are believed to have caught the virus from the first case confirmed last week, a 68-year-old man who had traveled to Bahrain in April and May, and returned to South Korea via Qatar.

The Health Ministry said the son of the second confirmed victim in the outbreak, who was himself being observed for possible infection, broke voluntary home quarantine and left South Korea on Tuesday for China.

"We should have checked more actively and broadly on family related issues. We are deeply sorry about that," Yang Byung-kook, director of the Korea Centers for Disease Control and Prevention, told reporters.

Chinese authorities are investigating the whereabouts of the suspected victim and are expected to announce their results as early as Thursday, he added.

First identified in humans in 2012, MERS is caused by a coronavirus from the same family as the one that triggered China's deadly 2013 outbreak of Severe Acute Respiratory Syndrome. There is no cure or vaccine.

Last week, South Korea's Health Ministry said there were 1,142 cases of MERS in 23 countries and 465 deaths had been reported by May 16. Of the total, 1,117 were in the Middle East.