Ómicron has also been detected in Botswana, Belgium, Hong Kong and Israel.
In the Netherlands 61 people who arrived in Amsterdam on two flights from South Africa tested positive for covid-19, Dutch officials said.
All were isolated in a hotel near Schiphol airport.
The Dutch authorities are carrying out more tests to see if among the infections any cases of Ómicron are detected.
Infected people were among 600 passengers who were held for several hours at the airport after their arrival, while they were being tested for the coronavirus.
Countries around the world have rushed to introduce travel bans and restrictions to southern African countries in an effort to contain the spread of Omicron.
The UK has put 10 countries on its travel red list, meaning that from Sunday, all people arriving from those places will have to quarantine in a hotel for 10 days.
On Friday, the UK included South Africa, Namibia, Zimbabwe, Botswana, Lesotho and Eswatini on the list.
In his announcement on Saturday, the health secretary said Angola, Mozambique, Malawi and Zambia would be added to that list.
He also said: “We have always been very clear that we will not hesitate to take further action if that is what is required.”
“Today I can announce that one thing we are doing immediately is conducting specific tests and sequencing the positive cases in the two affected areas.”
