The cases were discovered among 600 passengers who arrived at Amsterdam’s Schiphol Airport on two flights on Friday before the Dutch government halted air traffic from southern Africa due to concerns over the variant.
The passengers were kept separated from other travellers and those that tested positive are in isolation at a hotel near the airport.
Omicron has been designated a variant of concern by the World Health Organisation (WHO).
Experts said there is early evidence to suggest Omicron has an “increased risk of reinfection” and its rapid spread in South Africa suggests it has a “growth advantage”.
A spokesperson for the Dutch health ministry said it would not be known until later Saturday whether the passengers are infected with the new variant.
The variant has so far been detected in Belgium, Botswana, Israel and Hong Kong.
A German minister on Saturday said the variant had very probably arrived on its shores.
Authorities in Czech Republic are examining a suspected case of the Omicron variant that had been detected in a person who’d spent time in Namibia.
"A lab is checking a possible find of a positive specimen of the Omicron variant. We are awaiting confirmation or refutation of the case," spokesperson said in an emailed statement.
The United States, Canada and Russia have imposed travel restrictions on those entering from southern Africa.
NEW—“Dozens” likely infected onboard 2 flights ✈️ carrying ~600 people from South Africa that landed in Netherlands—Dutch health service estimates up to ~85 cases —so far 15 positive from 110 tested. Nearly 500 results still pending—& pending if #Omicron. https://t.co/kd7FaslXQX pic.twitter.com/GQvEVaGMyS
— Eric Feigl-Ding (@DrEricDing) November 27, 2021
The White House said the US will restrict travel from South Africa and seven other countries in the region beginning on Monday.
Mr Biden said that means "no travel" to or from the designated countries except for returning US citizens and permanent residents who test negative.
EU Commission president Ursula von der Leyen said flights will have to "be suspended until we have a clear understanding about the danger posed by this new variant, and travellers returning from this region should respect strict quarantine rules".
She warned that "mutations could lead to the emergence and spread of even more concerning variants of the virus that could spread worldwide within a few months".
"It’s a suspicious variant," said Frank Vandenbroucke, health minister in Belgium.
"We don’t know if it’s a very dangerous variant."
Israel, one of the world’s most vaccinated countries, announced on Friday that it also detected its first case of the new variant in a traveller who returned from Malawi.
The traveller and two other suspected cases were placed in isolation.
A three-week partial lockdown began on November 13 in the Netherlands amid surging Covid-19 cases.
Under the lockdown, bars, restaurants and supermarkets will have to close at 8pm (7pm GMT), professional sports matches will be played in empty stadiums and people are being urged to work from home as much as possible.
Stores selling non-essential items will have to close at 6pm.
Despite the country having a 72 percent double-vaccination rate, an average of 47 patients are admitted to intensive care per day, according to the Dutch agency for disease control and prevention (RIVM).
The RIVM has reported an average of 22,258 daily positive cases over a seven-day period.