It appears likely that Public Health director Mark Veitch will extend the public health emergency declaration for a further three months before it expires on January 12.

The declaration allows Dr Veitch to authorise requirements for quarantine and isolation, masks, density restrictions, and testing and tracing. Without it, the Public Health Act only provides the power to act on individual people, rather than groups or the whole population.

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The World Health Organisation this week detailed how the Omicron variant spreads "at a rate we have not seen with any previous variant", and that even a less severe disease could overwhelm health systems if it spread uncontrolled.

NSW COVID cases increased from 840 to 1360 in one day.

Vaccines could also have reduced effectiveness against infection, with the WHO highlighting the need to continue using masks, hand hygiene, ventilation and social distancing.

Dr Veitch said authorities were monitoring the situation internationally and on the mainland.

"We look every day at what the risk is from overseas, and looking at the risk both within Australia, we look at Victoria and NSW data obviously particularly at the moment, but all around Australia," he said.

"It's changing very quickly at the moment because of Omicron.

"I think it's too soon when [international arrival] requirements will change, but the things that will influence the decision are when we have a better understanding of the severity of Omicron, and when the Omicron spread across the world stabilises or at least takes on a recognisable pattern."

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International arrivals must provide a negative COVID test 72 hours before travelling and then quarantine - including at home - for seven days if vaccinated. This increases to 14 days for the unvaccinated, if given approval to enter Tasmania.

The public health emergency declarations were likely to continue until the overall COVID risks had subsided.

"Once we move to a situation where we're living in a highly vaccinated world with COVID circulating at a level that doesn't require substantial public health measures, that will be the sort of time that we would be able to look to cease the public health emergency declaration," Dr Veitch said.

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