Enele Sopoaga said most people living on the outer islands had been severely affected, with houses and crops being washed away and at least one island being entirely flooded.
Tuvalu has a population of 9876 at the last census in 2013.
He said there was a health and safety concern following some cemeteries being destroyed.
“Forty five percent of the population of Tuvalu, most of whom are on the outer islands, have been affected, badly, severly affected. We are worried about the aftermath in terms of hygeine and supplies of essential materials like food, medicine and water.”
Sopoaga said government boats would travel to the outer islands to assess the extent of the damage and hand out emergency supplies.