A coronavirus “variant of concern” has now been detected in major cities – including Sydney and London – as more countries move to restrict travel.

About 260 people who arrived in New South Wales on the same flight as two passengers who have tested positive to the Omicron variant must now isolate.

Authorities have informed them they must stay home for 14 days regardless of whether they test negative.

Both Omicron-positive passengers, who travelled on Qatar Airways QR908 from Doha on Saturday night, are in isolation in the Special Health Accommodation.

They had already been fully vaccinated against the coronavirus and did not have symptoms.

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Victoria’s health department said one person who has tested positive to the coronavirus in NSW after visiting a “country of concern” had also been in Victoria.

“Returned travellers to Victoria from countries of concern have been tested, and only negative tests have been received so far,” the department said.

“Victoria is also aware of a case who has returned to Australia from a country of concern and tested positive in NSW.

“The case travelled to Victoria from NSW and subsequently returned to NSW.”

Meanwhile, British authorities confirmed early on Monday morning that they have found a third case of Omicron, this time in a person who visited central London but has since left the country.

They are moving to tighten some health rules, including telling high school students they must wear face masks in communal areas.

The first British cases were linked to Brentwood, Essex and Nottingham. The third person had visited Westminster in the heart of London.

Officials said the cases were linked and connected to travel in southern Africa, the BBC reported.

In the Netherlands, 13 cases of the Omicron coronavirus variant were found among passengers who were on flights from South Africa that arrived in Amsterdam on Friday.

The Dutch government had already announced prior to the Omicron outbreak it was restricting evening activities following a sharp rise in the number of COVID-19 infections and patients needing hospital treatment.

The evening lockdown – beginning on Sunday – means shops, cultural venues, restaurants and sports clubs are required to close at 5pm.

Austria continues to investigate a suspected case and in France Health Minister Olivier Veran said the new variant was probably already circulating there. A third Omicron case has also emerged in Germany.

The discovery of Omicron, dubbed a “variant of concern” last week by the World Health Organisation, has sparked worries around the world that it could resist vaccinations and prolong the nearly two-year COVID-19 pandemic.

About 260 passengers and airline crew who arrived in Sydney on Saturday must now isolate. Photo: AAP.

First discovered in South Africa, the variant has since been detected in Britain, Germany, Italy, Belgium, Botswana, Israel, Hong Kong – and now Australia.

By Monday, Morocco has become the latest country to restrict travel in response to the emergence of the mysterious variant.

Its Foreign Ministery confirmed all incoming air travel from around the world would be suspended, to “preserve the achievements realised by Morocco in the fight against the pandemic, and to protect the health of citizens”.

Morocco kept its borders closed for months in 2020 because of the pandemic, fearing that its health system wouldn’t be able to manage the surges of patients seen in nearby Europe.

The kingdom in North Africa has had among Africa’s highest rates of confirmed infections but also is at the forefront of the continent’s vaccination effort, with 66 per cent of its population having received at least one dose.

The flight suspension was among the most dramatic of many restrictions being imposed by nations around the world as they scramble to slow the Omicron variant’s spread.

Many countries have imposed, or are planning, restrictions.

In the most far-reaching effort to keep the variant at bay, Israel announced late on Saturday it would ban the entry of all foreigners and reintroduce counter-terrorism phone-tracking technology to contain the spread of the variant.

New Australian cases prompt restrictions

Some 29 people who had been in one of the nine southern African countries subject to elevated restrictions touched down in Sydney across two flights on Saturday evening.

They have all been sent to hotel quarantine.

OMICRON VARIANT CONFIRMED IN NSW CASES pic.twitter.com/s0Z4hWYsSH

— NSW Health (@NSWHealth) November 28, 2021

NSW Premier Dominic Perrottet said the confirmation of the Omicron variant being in Australia is a reminder that the pandemic is not over, and described his approach as precautionary.

However, he cautioned that it must be expected that the variant will spread throughout the world.

“We need to learn to live alongside the virus. We need to learn to live alongside the variants of the virus,” he said.

Although he’s ordered all international arrivals to quarantine at home for 72 hours, Mr Perrottet insisted the NSW international and state borders would remain open.

“We can’t be a hermit kingdom on the other side of the world,” he said.

“There’s only so much governments can do. The best thing we can do as a people is to get vaccinated, get a booster shot, and that will keep you and your family safe.”

The three-day quarantine order is on top of a federal government requirement for travellers to enter quarantine for two weeks if they’ve been in South Africa, Lesotho, Botswana, Zimbabwe, Mozambique, Namibia, Eswatini, Malawi or the Seychelles within the past 14 days.

There are no plans to adjust the state’s reopening roadmap, Mr Perrottet said, so restrictions will still ease for the unvaccinated on December 15.

-with AAP