Tropical Cyclone Osai is the second cyclone in a week passing the Cook Islands, while there is an orange alert for parts of French Polynesia due to cyclone Nat.
In Bua, some people had to flee as their houses disintegrated in the wind.
In Koro, destructive winds and heavy rain are being felt in Nasau Village and people have been relocated to two evacuation centres.
Panapasa Nayabakoro, who lives in Koro, said 32 people are sheltering at the Nasau Health Centre and the rest are in a school. He said most of their houses are flooded and some were houses blown away.
A teacher at Nacamaki District School in Koro, Ilisabeta Daurewa, said they are experiencing damaging winds and several kitchen sheds in the village have been blown away.
She said more than 100 people are taking shelter in six classrooms at the school.
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