NEW YORK, United States --- New York Mayor Bill de Blasio on Monday announced a blanket Covid-19 vaccine mandate for the private sector in the United States' biggest city, starting from late December.

The order goes further than a nationwide mandate set by President Joe Biden for companies with more than 100 employees to vaccinate workers by January 4 that has been stalled by court suspensions.

"As of today we are going to announce a first-in-the-nation measure -- our health commissioner will announce a vaccine mandate for private sector employers across the board," de Blasio said on MSNBC, adding that it would take effect December 27.

Vaccine mandates have a long history in the United States but have generally been issued by cities or states.

De Blasio cited the emergence of the Covid-19 Omicron variant, cold winter weather and holiday gatherings as "additional challenges" to tackling the pandemic in New York, which was hard hit by the virus in 2020, with at least 34,000 deaths.

Omicron cases have been confirmed in at least 15 US states since it was first reported in late November, including several in New York, with de Blasio saying he was "very concerned."

"We in New York City have decided to use a pre-emptive strike to really do something bold to stop the further growth of Covid and the dangers it's causing to all of us," he said.

- Mixed public reaction -

Apart from the mandate, which would cover some 184,000 business and companies, he said there will be other measures to "focus on maximizing vaccination quickly so we can get ahead of Omicron and all the other challenges we are facing right now with Covid."

For indoor dining, gyms and entertainment venues, children aged five to 11 will have to show proof of one vaccination dose. All New Yorkers aged 12 and older will be required to show proof of two vaccine doses for the same venues.

Children aged five to 11 must also be vaccinated for "high-risk" extracurricular activities such as sports and music.

"I think it's a good idea," Sarah Dejam, 30, who works in the legal sector, told AFP. "There are a lot of people out there that are getting sick from the virus and all of its variants even with the vaccine."

But many others criticized the mayor, a Democrat who has less than a month left in office.

New York resident Jeff Bollerman said "it's extreme -- it seems to be ham fisted and (it) seems to be overkill."

The United States has imposed a travel ban on South Africa and seven other southern African countries to stem the variant spread.

Biden on Thursday unveiled his latest plans to battle Covid-19 during the winter, with new testing requirements for travellers and a surge in vaccination efforts.

All incoming travellers will need to test negative within a day of their flights, and rapid tests that cost $25 will be covered by insurance and distributed free to the uninsured.

Widespread vaccine hesitancy has thwarted US efforts to end the pandemic despite injections being free and easily available.

Even with ever-more creative attempts to encourage people to get their shots, about 40 percent of the United States have yet to be fully vaccinated, and booster rates are also lagging.

Top US pandemic advisor Anthony Fauci said Sunday that early indications of the severity of the Omicron variant were "a bit encouraging" but cautioned more information was still needed.