Kiribati and Samoa entered lockdowns Saturday after overseas arrivals brought COVID-19 to the Pacific island nations that had avoided the worst of the pandemic for two years.
Until this month, Kiribati hadn't reported a single virus case, while Samoa had only recorded two since the pandemic began, according to the World Health Organization.
But authorities in both countries have been forced to put in place stay-at-home orders after the virus was detected in international arrivals.
Dozens of passengers on a flight to Kiribati from Fiji -- the first to arrive in the nation since borders reopened -- tested positive for the virus.
And in Samoa, the restrictions were triggered after cases linked to a repatriation flight from Brisbane rose to 15, prime minister Fiame Naomi Mata'afa said.
"The measures outlined are not intended to cause panic, but to simply encourage caution, vigilance and enhance awareness of an evolving situation," she said.
The restrictions will lift on Monday night and all current cases - believed to be infected with the Omicron variant - are in quarantine, she added.
Kiribati's leader said the capital - home to almost half of the country's 120,000 population - would be placed under the restrictions after recording its first community cases.
"There is now an assumption that COVID-19 is now spreading in the community," President Taneti Maamau said in a statement on Facebook.
Under the restrictions, locals must stay home unless in need of essentials like food or healthcare.
It was unclear how long the lockdown would last, but a previous announcement said similar restrictions would end Thursday.
Around 62 percent of Samoa's population is fully vaccinated, while about 34 percent of Kiribati's population is double-jabbed, according to WHO data.