Europe stepped up vaccinations of children aged five to 11 against Covid-19 Wednesday, as the EU's health agency warned immunisation alone would not stop the rapid rise of the Omicron variant.

Croatia, Germany, Greece, Hungary and Spain were among those opening up their inoculation drives to younger kids, with other nations still weighing their approach.

South Africa -- where Omicron was first detected -- and Britain recorded their highest daily coronavirus case numbers Wednesday as Washington's top diplomat curtailed a tour of Southeast Asia after a delegate caught the virus.

At a hospital near Spain's capital Madrid, nurses wearing Christmas antler headbands welcomed children and gave them stickers after their shots.

Some German cities plan to administer kids' jabs in museums and zoos, while others are mulling mobile vaccination teams outside schools
Some German cities plan to administer kids' jabs in museums and zoos, while others are mulling mobile vaccination teams outside schools AFP / Tobias SCHWARZ

"It only hurt a little," said 11-year-old Magdalena Lazo Vitoria as she left the vaccination centre, a plaster on her left shoulder.

"I wasn't nervous because I wanted to get vaccinated for a long time now, so I am really happy."

The rapid spread of the heavily mutated Omicron variant lent fresh urgency to the push, as EU chief Ursula von der Leyen warned the new strain could be dominant in Europe by mid-January.

Even as children lined up to get jabs, the EU health agency ECDC said measures like mask-wearing, distance working and the prevention of crowds were essential to reduce the burden on healthcare systems in the time available, with vaccines alone taking too long.

The Pfizer-BioNTech vaccine is administered in a lower dosage and comes in a paediatric vial with an orange cap
The Pfizer-BioNTech vaccine is administered in a lower dosage and comes in a paediatric vial with an orange cap AFP / Tobias SCHWARZ

Spanish Prime Minister Pedro Sanchez said he hoped his country, which already has one of Europe's highest Covid-19 vaccination rates, would become an "example for the world" with its immunisation campaign for five to 11-year-olds.

The country has around 3.3 million children in that age group.

Police in Germany's Saxony state have responded to threats against politicians
Police in Germany's Saxony state have responded to threats against politicians AFP / John MACDOUGALL

Doctors across Europe reported strong initial demand from parents.

"As soon as we offered the vaccine appointments, they were pretty much all snapped up," said Jakob Maske, a Berlin-based doctor and spokesman for Germany's association of paediatricians.

Germany's STIKO vaccine commission has officially only recommended the jab for children with pre-existing conditions, but even healthy children will be inoculated if the parents request it.

Some German cities plan to administer kids' jabs in museums and zoos, while others are considering mobile vaccination teams outside schools.

Vaccines dosed for children are marked with an orange colour to set them apart
Vaccines dosed for children are marked with an orange colour to set them apart SPAIN HEALTH MINISTRY via AFP / Handout

But like other countries, Germany also grapples with anti-vaccine militancy and Wednesday saw police in the eastern city of Dresden stage raids over death threats against Saxony state's pro-vaccine premier Michael Kretschmer.

While serious illness and death from Covid among children is rare, those infected can pass the virus to other people at higher risk of serious illness, such as the elderly.

The EU's medicines watchdog last month approved the lower-dosage Pfizer-BioNTech shot for five- to 11-year-olds, an age group experiencing high coronavirus infection rates across the continent.

Denmark, which has seen a surge in cases attributed to the new Omicron variant, and some Austrian regions already began offering jabs to younger kids in November.

The United States was the first large country to take the plunge and has so far vaccinated more than five million children in the 5-11 age bracket.

US Secretary of State Antony Blinken on Wednesday cut short a visit to Thailand after a member of his delegation contracted coronavirus.

Several European nations are tightening virus restrictions, with Poland imposing limits on the number of people allowed in restaurants, hotels and theatres.

Britain on Wednesday registered 78,610 laboratory-confirmed cases, its highest total of the pandemic, a day after lawmakers approved stricter curbs in England amid estimates of 200,000 daily Omicron infections.

The English Premier League also suffered more disruption as a coronavirus outbreak within Watford's squad forced their match against Burnley to be postponed less than three hours before kick-off.

Italy will from Thursday tighten restrictions for arrivals from the rest of the EU, requiring coronavirus tests for all travellers, while Greece announced a similar measure to come into effect from Sunday.

A number of European countries will launch children's vaccination drives in the coming days, including Italy, Portugal, Poland, the Baltic states and the Czech Republic, while others are still finalising their plans.

In France, vaccination has only been approved for five to 11-year-olds at risk of developing serious illness, but the government has said it is considering extending it to all children on a voluntary basis.

Belgium is awaiting the recommendation of its national health body, with a rollout likely around the new year.

British regulators are still assessing whether to approve jabs for the 5-11 age group, with a decision likely before Christmas.

Oil prices fell further amid fears of weakening demand caused by the spread of Omicron.