Sixty-one people from two flights from South Africa to the Netherlands have tested positive for the coronavirus, Dutch health officials said early Saturday. It was unclear as of late morning local time if the cases were linked to the newly discovered Omicron variant.

The health officials tested 600 passengers who arrived on Friday morning at Amsterdam’s Schiphol Airport. Those who tested negative were allowed to leave the airport and quarantine at home, or to continue their journeys.

When the Netherlands announced its travel restrictions on flights from southern Africa, the two KLM flights were already on their way to Schiphol. About half an hour before the first one landed, health officials were dispatched to the airport to conduct the tests there, said Harm Groustra, a spokesman for the GGD, the Dutch public health service.

One of the passengers stuck on the tarmac was the New York Times reporter Stephanie Nolan, who had been in South Africa covering the country’s response to the pandemic.

“So I’m in my 3d hour on a tarmac at Schiphol,” she tweeted, after her flight from Johannesburg had landed. “While my flight from Jo’burg was somewhere over Chad, Europe went into variant panic; by the time we landed, we weren’t allowed off the plane.”

Many passengers had ignored mask requirements, she said.

Dutch health officials said in a statement that they understood frustration among passengers who had thought that they would be allowed to go home, but were instead “confronted with a situation like we’ve never had before in the Netherlands.”

Hugo de Jonge, the country’s health minister, tweeted that those with a positive test were being taken to a quarantine hotel near the airport. “Now it’s important to research whether this concerns the Omicron variant,” he wrote.

People who tested positive have to stay at the hotel for at least seven days if they have symptoms, or for five days if they do not, health officials said. Passengers who had tested positive for the coronavirus and live with people who were on the flight will be allowed to spend their quarantine at home.

Cases have been rising quickly in the Netherlands, which yesterday announced stricter measures to try to curb the spread of the virus, including an evening lockdown that starts at 5 p.m. Last week, almost 154,000 people tested positive, a 39 percent increase from the week before.

“The number of coronavirus infections has never been as high as in the past week,” the government said on Friday, adding that the caseload was at risk of overwhelming hospitals in the country.

Jason Horowitz contributed reporting.