Initial investigations have shown that a traveller who tested positive for Covid-19 in South Korea after transiting in Changi Airport was unlikely to have been infected in Singapore, said the authorities yesterday.

"The source of infection remains unknown and investigations by the various authorities are ongoing," said the Ministry of Health (MOH) and the Civil Aviation Authority of Singapore (CAAS) in a joint statement.

"As an added precaution, contact tracing in Singapore is also under way."

The man left New Zealand on July 21 and arrived in South Korea on July 22, when a polymerase chain reaction test done four hours after his arrival showed he was positive for the virus.

The South Korean authorities subsequently informed New Zealand that they suspected the man, who showed no symptoms, had been infected during transit at Changi Airport. But this would have meant an incubation period of less than 24 hours, the Singapore authorities said.

According to the World Health Organisation, the average incubation period for Covid-19 is five to six days, up to a maximum of 14 days.

"Singapore is in contact with the New Zealand and South Korea authorities for further information," said MOH and CAAS.

The New Zealand Herald reported yesterday that the infected person was a 22-year-old man who had travelled to various parts of the country, and had gone on a bus tour and a boat cruise.

The health authorities there have been carrying out contact tracing and testing to rule out community transmission, it said.

In Singapore, stringent measures are in place to ensure that passengers transiting through Changi Airport are segregated from all other passengers at all stages of their journey, the authorities said.

Airport staff wear personal protective equipment when interacting with passengers, while passengers are required to wear masks at all times.

"Safe distancing, temperature taking for passengers and staff are also enforced," they said. "All transit passengers, including those who had arrived on the same flight as the individual, adhered to these precautionary measures."

Travellers have been allowed to transit in Changi Airport since June 2. Upon their arrival in Singapore, transiting passengers are directed to special holding areas.

Seats in these areas are vacuumed and wiped regularly with disinfectant, while frequently touched surfaces have been sprayed with long-lasting anti-microbial disinfectant coating.

Contactless hand sanitiser stations are also available.