A deadly respiratory disease has sparked widespread panic across South Korea after claiming its first victims in the largest outbreak outside the Middle East.

A 58-year-old woman died of acute respiratory failure yesterday and tests later came back positive for MERS (Middle East Respiratory Syndrome), the health ministry said.

The other victim was a 71-year-old man who was confirmed to have the virus several days ago and who died on Tuesday.

Six more South Koreans were diagnosed with the MERS virus Monday night, the ministry said, bringing the total number of people infected to 25 including the two deceased.

Around 750 people who were exposed directly or indirectly to the virus have now been placed under mandatory or voluntary quarantine.

South Korean hospital workers a man in front of a quarantine tent erected for suspected MERS cases at the Seoul National University Hospital in Seoul on Tuesday. South Korea's health ministry confirmed that two people have died from Middle East Respiratory Syndrome (MERS), the country's first fatalities from the virus

Widespread panic: Passengers wearing masks to prevent contracting Middle East Respiratory Syndrome (MERS) ride on a travelator upon arrival at Incheon International Airport in South Korea on Tuesday amid the largest outbreak of the virus outside the Middle East

First line of defence: A quarantine officer checks the body temperature of a passenger as they walk past a thermal imaging camera at Incheon International Airport. South Korea on Tuesday reported its first two deaths from an outbreak of Middle East Respiratory Syndrome that has infected 25 people in two weeks

Previously, the only other fatal MERS case in Asia was a man who died in Malaysia in April 2014.

The first case – a 68-year-old man diagnosed after returning from a trip to Saudi Arabia – was reported on May 20.

Health Minister Moon Hyung-Pyo appealed to anyone placed under voluntary quarantine for the two-week incubation period to observe isolation guidelines.

'Those who are quarantined must be experiencing a lot of inconvenience in their daily lives, but please closely co-operate for the safety of yourself, your families and your neighbours,' Moon said.

He also urged citizens to wear surgical face masks in public places and to wash their hands frequently in order to ward off infection.

The outbreak has been met with growing public alarm, and online retailers reported a 700 per cent surge in sales of face masks over the weekend.

On Seoul stock markets, share prices of some pharmaceutical firms jumped by the daily limit of 15 per cent on Tuesday, while those of airline and travel operators took a dive.

Fear: Chinese tourists wearing protective facial masks walk on a street in Seoul, South Korea, on Tuesday

A couple wear masks as a precaution against Middle East Respiratory Syndrome (MERS) virus as they walk on a street in Seoul, South Korea. The outbreak has been met with growing public alarm

Concerns will be further fuelled by the health ministry's announcement that two of the new cases involved tertiary infections.

Previously, all the infections had involved patients in the same hospital as the initial carrier, their relatives or hospital staff with whom he came into contact.

'We are tracking down additional cases (of tertiary infection)... with the possibility of more new infections in mind,' said Kwon Jun-Wook, a senior health ministry official leading an emergency task force team.

More are expected to be quarantined or put under observation, Kwon said, adding that some 240 people had been banned from travelling overseas.

Three patients are currently in critical condition, he added.

Acting prime minister Choi Kyung-Hwan vowed 'all-out efforts' to curb the spread of the virus, citing public concern that the initial response had been 'poor'.

'We should use all our national resources to alleviate public concerns,' he said.

Hospital workers set up an emergency center for MERS cases at the National Medical Centre in Seoul

Citizens to wear surgical face masks in public and to wash their hands frequently to ward off infection

Deadly: A graphic explaining the MERS virus which appears to have been passed to humans by camels

A medical worker enters a quarantine tent for suspected MERS cases at Seoul National University Hospital

One primary school in Gyeonggi province, located near the hospital where the female victim died, closed down temporarily as parents withdrew their children.

According to the Yonhap news agency, dozens more schools in the area were also considering temporary shutdowns.

Middle East Respiratory Syndrome 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.

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

South Korean President Park Geun-Hye has scolded health officials over their 'insufficient' response to the outbreak.

The authorities 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 Friday to have been infected himself.