There are 116 people infected on the island - 36 imported and 80 local cases.
Nine new cases have been found in Butaritari Island, prompting the government to advise local authorities to enforce a lockdown.
Several other islands have been placed under strict restrictions - including South Tarawa, Betio, and Buota - to stop the virus from spiralling out of control.
Meanwhile, the government said that from today, fishermen in South Tarawa and Betio would only be allowed to go fishing between 6am and 2pm.
Only four people would be allowed to be on a boat or part of a group fishing near shore, it said.
The government has declared a state of disaster and the entire nation - of 120,000 - is on lockdown under a strict 24-hour curfew.
Speaking to RNZ Pacific from Tarawa, freelance journalist Rimon Rimon said the increase in positive cases had caused "real fear in the community".
"That's the initial reaction that people have, when their life is in danger, they panic you know. That's certainly the situation in Kiribati," he said.
Kiribati was among a handful of countries that were Covid-19-free, mainly because it kept its borders shut to the outside world for almost two years.
Over 93 percent of its eligible population has been vaccinated, while just over 50 percent are fully vaccinated.
But the nation is well short of its target of inoculating 80 percent of its target population, even though the government announced in September 2021 it had enough vaccines to immunise more than 70,000 people over 18 years old.
Rimon said while the vaccination programme was rolled out smoothly, it was not adequate for Kiribati to open its borders freely - as in the case of other countries.
"Once the government opened up its borders and brought in its flights that's when things changed completely. The change was pretty sudden on the people and also the government and we can see on the ground the response is not as efficient as people would want it to be."
It was still unclear how the virus spread into the community after a flight carrying 36 Covid-19 positive people arrived from Fiji on 14 January, he said.
"At the moment our Ministry of Health is on top of things but as I understand they are overwhelmed at the moment with resources and manpower."
Meanwhile, the authorities are advising people to strictly follow the Covid-19 protocols to minimise the risks and spreading the virus in the community.