New Zealand Prime Minister Jacinda Ardern was Sunday forced to call off her own wedding as she tightened Covid-19 restrictions in the face of an outbreak of the Omicron variant.

"My wedding will not be going ahead," she confirmed after detailing new restrictions; including a limit of 100 fully vaccinated people at events.

"I just joined many other New Zealanders who have had an experience like that as a result of the pandemic and to anyone who is caught up in that scenario I am so sorry."

The emergence of nine cases of Omicron in a family who travelled between cities to attend a wedding, and the infection of a flight attendant on one aircraft they flew on, forced New Zealand to impose its "red setting" restrictions from midnight Sunday.

Omicron is far more transmissible than the earlier Delta variant but is less likely to make people seriously ill.

In addition to limiting crowd numbers, face coverings are now mandatory on public transport and in shops.

Ardern and long-time partner Clarke Gayford have never announced their wedding date, but it was believed to be scheduled for some time in the next few weeks.

The new restrictions are set to remain in place until at least the end of next month. 

"Such is life," Ardern said when asked how she felt about setting regulations which ended her planned nuptials.

"I'm no different to thousands of other New Zealanders who have had much more devastating impacts felt by the pandemic, the most gutting of which is the inability to be with a loved one sometimes when they are gravely ill. That will far outstrip any sadness I experience."

New Zealand has detected 15,104 Covid-19 cases and recorded 52 deaths since the pandemic began.

Tough border restrictions and snap lockdowns have been in place for much of the last two years. 

Beijing tests two million

Beijing city officials on Sunday said all two million residents of a neighbourhood where they identified a small cluster of Covid-19 infections will be tested, less than two weeks ahead of the start of the Winter Olympics.

The announcement came days after China's postal service ordered workers to disinfect international deliveries after authorities claimed mail could be the source of recent coronavirus cases.

Some 30 infections have been detected in the past week in Beijing, one of the world's most populous cities.

Both the WHO and the US Centers for Disease Control have said the risk of being infected from contaminated surfaces is low.

China's cases constitute a tiny fraction of the massive surge in countries around the globe, with the highly contagious Omicron variant driving a fresh spike in infections.

Still, multiple small outbreaks around China -- including in Beijing -- have tested the country's strict "zero Covid" policy, which authorities have pursued even as the rest of the world has gradually reopened.

Local authorities have identified Fengtai district in southern Beijing as the epicentre of a cluster of six new confirmed infections, taking the number of cases in the capital to 34.

All two million of the area's residents will be tested for Covid-19 starting from Sunday.

With the Beijing Games starting on February 4, international delegates, media personnel, and some athletes have already begun arriving.

In an effort to thwart the coronavirus, China is sealing the Olympics inside a tightly controlled bubble cocooning thousands of people and stretching nearly 200 kilometres (120 miles).