Air travel continued to be severely disrupted in the United States on Saturday, with bad weather in parts of the country adding to the impact of a massive spike in Covid-19 infections fuelled by the Omicron variant.

The United States had 2,723 cancelled flights, more than half of the 4,698 cancelled worldwide, around 11:00 pm (0400 GMT Sunday), according to tracking website FlightAware. 

In addition, 5,993 domestic flights were delayed on Saturday, out of a total of 11.043 worldwide for the day.

The worst affected US airline was SkyWest, which had to cancel 23 percent of its flight schedule, according to the site.

In the United States, airports in Chicago were particularly hard-hit because of bad weather, with a snowstorm expected in the area on Saturday afternoon and into the night.

The global air travel industry is still reeling from the highly contagious Omicron variant.

Many pilots, flight attendants and other staff are absent from work after contracting Covid-19, or because they are quarantining after coming in contact with someone who has the infection.

Some 7,500 flights were cancelled by airlines worldwide over the Christmas weekend.

England curbs 'last resort'

Britain's health minister insisted Saturday reimposing coronavirus restrictions in England would be "an absolute last resort" and that the country must "try to live with Covid".

The country is among those in Europe hardest hit by the pandemic, registering nearly 149,000 deaths. It counted almost 163,000 new cases Saturday, a slight dip after days of unprecedented daily tallies.

The UK government, which has responsibility for health policies in England only, has so far refused to curb socialising and large events, unlike the rest of Britain.

Northern Ireland, Scotland and Wales have all rolled out new rules since Christmas limiting gatherings, as the Omicron variant fuels an unprecedented nationwide surge in infections.

But Prime Minister Boris Johnson's government in London insists the data does not yet justify such measures in England.

"Curbs on our freedom must be an absolute last resort and the British people rightly expect us to do everything in our power to avert them," Health Secretary Sajid Javid wrote in the Daily Mail newspaper.

"I've been determined that we must give ourselves the best chance of living alongside the virus," he added, noting the "enormous health, social and economic costs of lockdowns".

Despite the record rise in infections, there has been a less dramatic rise in numbers admitted to hospital and then intensive care units, fuelling hopes that Omicron is less severe.

"I've been working closely with the NHS, to make sure it is ready and resilient for what lies ahead," Javid vowed.

- 'Watch and wait' -

In England, the government last month mandated mask-wearing in most settings, working from home if possible and a Covid pass system for nightclubs and large events.

But it has stopped short of the further measures seen in other parts of the UK.

Instead, it is relying on a stepped-up vaccination programme, which saw every adult offered a third dose by end-2021 and around 60 percent of the eligible population getting a booster jab.

However, Education Secretary Nadim Zahawi said late Saturday the government would recommend secondary school students wear face coverings in classrooms and teaching spaces when they return next week as a "temporary" measure.

Writing in the Sunday Telegraph, he also conceded that "some remote learning will be necessary" as staff and pupil absences rise.

Meanwhile, the state-run National Health Service (NHS) is under increasing strain across Britain as hospital admissions reach levels not seen since last March.

Nearly 2,000 new patients were admitted in a single day earlier this week, according to the latest data released Saturday.

At the same time, more than 110,000 staff -- nearly one in ten NHS workers nationwide -- were absent from work Friday, the Sunday Times newspaper reported.

The Times said around 50,000 of those absent NHS workers were sick or self-isolating because of Covid-19.

"We still need to watch and wait," Chris Hopson, the head of NHS Providers which represents hospitals in England, tweeted.

But he added: "Govt must be ready to introduce new restrictions at pace if they're needed."

France to relax isolation rules

France will relax Covid isolation rules from Monday, the government announced, in a bid to ease their impact on society and the economy.

Fully vaccinated people who test positive will only have to isolate for seven days regardless of the coronavirus variant they were infected with, but can leave quarantine after five days if they show an antigen or negative PCR test.

There will be no quarantine for fully inoculated individuals who have a close contact test positive.

However, people must respect protective measures and "undergo regular testing", health minister Olivier Veran said in an interview with Le Journal du Dimanche.

Until now, those who tested positive in France had to isolate for 10 days with their close contracts also quarantined for a week.

The maximum isolation period could be up to 17 days -- regardless of the variant -- if a household contains a positive case. 

The change in rules responds to the need "to take into account the extremely rapid evolution of the spread of the Omicron variant in France". 

It should allow a "benefit-risk balance aimed at ensuring the virus is controlled while maintaining socio-economic life", said the Ministry of Health.

Additionally, "the first available virological data" showed "the incubation period of Omicron appears to be faster than previous variants, favouring a possible reduction in the length of isolation".

Meanwhile, people who test positive for the virus -- but who are not fully vaccinated -- must complete a 10-day quarantine, according to the same rules, but shortened to seven should they present a positive antigen or negative PCR test.

The seven-day quarantine remains for close unvaccinated contacts, who must show a negative test to leave isolation.