At least six Bangladeshi nationals and two South Koreans have tested positive for the coronavirus after entering South Korea on the same flight from the South Asian country, authorities said Friday.

All of the eight patients, including three Bangladeshi students enrolled in a Jeju university, used Korean Air flight KE9656, which landed at Incheon International Airport, west of Seoul, at 5:32 a.m. Thursday after departing from Dhaka, the capital of Bangladesh.

They then traveled to their homes or other residences around the country before taking COVID-19 tests at testing centers in Jeju, Incheon, Paju, Namyangju and North Jeolla Province, authorities said, noting epidemic research has been launched for the airplane and all of its passengers.

The three students are part of a group of 18 Bangladeshis enrolled in Cheju Halla University, who flew into Jeju International Airport on Thursday afternoon via the Incheon airport and Seoul's Gimpo International Airport to return to their campus on the southern resort island.

All of the 18 students took COVID-19 tests on landing at the Jeju airport and three of them tested positive, Jeju's provincial government said, noting that none of them showed symptoms of the virus at that time.

Another student's test was inconclusive, as it was difficult to judge his test result because it is located between positive and negative reference values, saying an additional test is due within several days. The remaining 14 students tested negative.

The Bangladeshi students are known to have used four different flights to travel from the Gimpo airport to Jeju after taking taxis from the Incheon airport to the Seoul airport. The three infected students arrived at the Jeju airport via T'Way flight TW713 at 12:52 p.m. and Jeju Air's flight 7C117 at 1:44 p.m.

In addition, three Bangladeshi migrant workers tested positive for the coronavirus in Incheon, Paju, just north of Seoul, and Namwon, North Jeolla Province, respectively, after arriving there via the same Korean Air flight Thursday. But four other Bangladeshis who traveled with the Paju worker tested negative.

According to authorities, a 13-year-old Korean boy, who boarded the same Korean Air flight to return home from Bangladesh, tested positive for the virus at a community health center near his home in Namyangju, a Gyeonggi city east of Seoul. The boy has reportedly attended school in Bangladesh since last August. Coronavirus tests are planned for his family members who were ordered to self-isolate at their home.

They also said a Korean man in his 40s was declared infected with the coronavirus Friday, while self-isolating at his home in Gwangju, southeast of Seoul, after returning here the previous day from Bangladesh aboard KE9656. But his wife and two daughters tested negative.

Earlier this week, two foreigners were found infected with the coronavirus after arriving in Yangju, north of Seoul, from Pakistan and the Philippines, respectively.

Under the compulsory quarantine measures, all entrants from overseas -- both Koreans and foreigners -- are obliged to self-isolate at their residences or government-designated facilities for 14 days.

On Friday, South Korea reported 49 new cases, including 17 imported ones, raising the total caseload to 12,306, according to government data. The daily number of imported cases marked the highest level since April 12, when 24 from abroad tested positive.

Recently, the number of foreign migrant workers entering South Korea has spiked due to rising labor demand in fishing and farming communities.

Quarantine authorities are concerned about a fresh nationwide spread of the virus from the latest arrivals from Bangladesh, as the Korean Air plane had 284 seats, though the actual number of its passengers is not yet known.

They fear more confirmed cases may emerge among other Korean Air passengers, as well as among people who came into contact with the infected passengers during their movements in local communities or on public transport.

Local authorities are also looking into possible routes of virus transmission among the passengers, as they may have been infected in Bangladesh or during the boarding process at Dhaka's airport.

"It is likely that the air passengers (from Bangladesh) may have been infected in the country of departure and entered (South Korea) without any symptoms or with light symptoms, instead of contracting the virus during flight or in the entry process," Jeong Eun-kyeong, director of the Korea Centers for Disease Control and Prevention (KCDC), said in a media briefing.

The KCDC said the coronavirus pandemic has been rapidly spreading in Southeast Asia, India, Pakistan and Bangladesh.

Bangladesh, for instance, has recently reported a surge in COVID-19 patients, with its cumulative number of confirmed cases tallied at 94,481 as of Thursday, compared with 83,293 in China, 41,216 in Singapore, 40,400 in Indonesia and 26,781 in the Philippines. The number of daily new infections in Bangladesh exceeded 3,000 for three days in a row this week.

"There could be an explosive increase in coronavirus cases (in Bangladesh), as coronavirus tests are reportedly conducted for some seriously ailing patients in the country. Some entry restrictions appear needed in this situation. Otherwise, it is necessary to consider requiring a COVID-19 negative certificate from people who have an unavoidable reason to enter (South Korea)," said a university professor in Seoul. (Yonhap)