There are 55 new Covid-19 cases in the community today. 

Whole genome sequencing has detected five further cases of Omicron in international arrivals, taking New Zealand's total to 13 cases with the variant, the Ministry of Health said in today's 1pm update. 

Today's update comes as experts call for tightened managed isolation restrictions to keep Omicron out of the community for as long as possible. 

Melbourne University epidemiologist Professor Tony Blakely says vaccines alone won't be enough, while Professor Michael Baker says pushing out next month's border reopening until February is just one of three measures he recommends to keep Kiwis safe. 

There are currently eight cases of the Covid-19 variant in New Zealand, all in managed isolation. 

Blakely told Newstalk ZB the risk of Omicron getting into the community was now seen as very high. 

Each day in New Zealand was a "roll of the roulette wheel in the casino of Covid". 

MIQ was better than it was, but is not perfect. 

Blakely said every time a new Omicron person was found in MIQ, there's a risk it's going to jump out. 

He said things like vaccinating all workers aren't that great at stopping a person from carrying Omicron out. 

Baker agreed, saying "MIQ would never be perfect due to the human factor" but that was why he wanted the Government take immediate action in halting next month's planned border reopening and instead push it out until February. 

He said we needed to continuously update our list of high-risk countries of where Omicron cases were coming from into New Zealand, and carry out more frequent testing of MIQ and port staff as well as air crew. 

They were all areas where Covid could - or has - snuck into the country as the source of any of the previous outbreaks was still not conclusively determined, he said. 

"One of the most important things is to look at the number of cases coming into MIQ and to adjust our travel policy accordingly." 

The length of time an Omicron person spent in MIQ had already increased from seven to 10 days, but that wasn't enough. 

"Every time an infected person arrives in MIQ you're increasing your risk of an escape from MIQ and it's also remembering that our three biggest outbreaks from now ... we don't the exact source of any of them. 

"We can't be totally sure it was only MIQ." 

Omicron should continue to be treated as severe until more was known about it and its impact on hospitalisations overseas. 

It was still the same virus and it's still transmitted the same way - via indoor aerosol and even fleeting contact. 

More should be known by New Year's Eve or New Year's Day as cases were now increasingly growing in Australia and the United Kingdom and it took roughly a week for the incubation period alone. 

"It's another two weeks before you get sick and or more whether people will start dying. 

"We've got a lag of about a month before you start to see the adverse effects. It could take even longer."