There are seven new cases of Covid-19 in managed isolation.

With stricter pre-flight Covid testing set to come into force this week, and a concerning drop in tracer app scans over the summer break, the Ministry of Health has revealed details on new infections coming into New Zealand.

There are no new cases in the community.

The new cases include three who arrived from Russia on January 6, and are part of the group of international mariners. In total, 17 positive Covid-19 cases have been identified in this group: nine are deemed historical and eight are active cases.

The four other cases arrived on January 7 and included one from India, two from the United States and one from Puerto Rico.

It comes as concerns mount around contagious new variants of the coronavirus from South Africa and the United Kingdom wreaking fresh havoc.

There are already 19 cases of the UK strain detected in New Zealand since December 13 and one case of the South African variant.

In recent days the number of active cases arriving in the country has spiked, with 31 people testing positive for the infection at the end of last week.

On Monday there were 77 active cases in New Zealand.

There have been no cases in the community since November 18.

For the second time in recent months, crew from a contingent of international seaman have tested positive for Covid. The ministry said 14 sailors had tested positive for the infection with eight deemed historical.

They are currently in a quarantine facility in Christchurch after arriving in the country a week ago.

Meanwhile the government is set to introducing fresh measures to combat community spread.

It included giving increased power to director-general of health Dr Ashley Bloomfield to require travellers from every country in the world to produce a negative Covid-19 test before they leave for New Zealand.

As well as this, most travellers will now be required to take a Covid-19 test as soon as they enter New Zealand.

At the moment, only people coming from the UK and the US are required to produce a negative test – but Bloomfield is set to expand that to every country in the world.

The only exceptions are travellers from Australia, Antarctica and some Pacific Island nations.

Covid response minister Chris Hipkins has also expanded New Zealand's domestic quarantine and isolation testing requirements.

From January 18, travellers from anywhere in the world will be required to undergo day 0/1 testing when entering the country, as well as the routine day 3 and 12 tests.

People travelling from Australia, Antarctica and some Pacific Island nations are also exempt from these rules.

From 11.59 pm Friday pre-departure testing will come into effect with the aim of reducing the number of cases of Covid-19 arriving in New Zealand.

Since the start of the year people arriving from the US and UK have been tested on arrival and required to stay in their room until they return a negative test result.