The COVID-19 Omicron variant was detected in the Netherlands before two flights arrived from South Africa last week carrying the virus, Dutch health officials said on Tuesday.

At least 14 people on flights from Johannesburg and Capetown arrived at Amsterdam's Schiphol airport on Nov. 26 carrying the new variant, the National Institute for Public Health (RIVM) said.

"We have found the Omicron coronavirus variant in two test samples that were taken on Nov. 19 and Nov. 23," the RIVM said. "It is not clear yet whether these people have visited Southern Africa."

The discovery of Omicron has sparked worries around the world that it could resist vaccinations and prolong the nearly two-year-old COVID-19 pandemic.

Some 61 out of the more than 600 passengers on the South Africa flights tested positive for COVID-19 and went into quarantine after arriving last Friday.

Dutch authorities are also seeking to contact and test some 5,000 other passengers who have travelled from South Africa, Botswana, Eswatini, Lesotho, Mozambique, Namibia or Zimbabwe.

In the Netherlands, tougher COVID-19 measures went into effect on Sunday to curb record daily infection rates of more than 20,000 and ease pressure on hospitals.