He said the declaration was subject to further review.
Mr Tu’i’onetoa said Tonga has closed its borders to everyone but citizens and residents in an attempt to stop the spread of coronavirus.
Kaniva News reports the government has banned indoor gathering of more than 20 and outdoor gathering of more than 40 people.
Weddings, funerals, concerts, kava clubs, nightclubs and sports are banned.
The measures did not apply to churches and schools.
Mr Tu’i’onetoa made the announcement during a news conference Thursday afternoon.