They were conducting further testing to see if any of the infections are with the recently discovered Omicron coronavirus variant.

About 600 passengers arrived on Friday at Amsterdam's Schiphol Airport on the two KLM flights and then faced hours of testing due to concerns over the new variant.

The Dutch health ministry said early on Saturday 61 tests had come back positive.

"Travellers with a positive test result will be placed in isolation at a hotel at or near Schiphol," health authorities said in a statement.

"Of the positive test results, we are researching as quickly as possible whether they are the new variant of concern, now named 'Omicron'."

The Dutch government banned all air travel from southern Africa early on Friday. Health Minister Hugo de Jonge determined that passengers already en route to the Netherlands would have to undergo testing and quarantine upon arrival.

Passengers on the two KLM flights, from Cape Town and Johannesburg, said they were kept waiting on the tarmac for hours.

A spokesman for the health authorities in Kennemerland, the Dutch region that oversees Schiphol, said the positive cases were being analysed by an academic medical hospital to determine whether they are the new strain.

The new variant has been detected just as many European countries are grappling with a surge in coronavirus cases.

The Dutch government separately on Friday announced the night-time closure of bars, restaurants and most stores as it tries to curb a record-breaking wave of cases that is swamping its healthcare system.

Australian Associated Press