Tropical Cyclone Gita struck Tonga as a Category 4 hurricane on Tuesday, the National Oceanic and Atmospheric Administration (NOAA) announced on Twitter. The Pacific island nation had declared a state of emergency in anticipation of the hurricane.

Before the storm hit, some residents nailed pieces of wood over their windows while others evacuated the island.

Weather experts said Gita was packing sustained winds of 195 kilometers per hour, about 121 miles per hour, and was expected to intensify before making landfall.

Tropical Cyclone #Gita hit #Tonga today with the strength of a Category 4 hurricane, the #Himawari8 geostationary satellite captured the path of the storm over the past 24 hours. Learn more about our international satellite partners in orbit here: https://t.co/SMSgTCxp0U pic.twitter.com/oefCA1fzZR — NOAA Satellites (@NOAASatellites) February 12, 2018

Publisher Pesi Fonua said there were dark clouds gathering overhead in the capital, Nuku'alofa, on Monday evening but few other signs that the storm was coming. He said people were busy nailing boards and roofing iron to their homes to try to limit the damage from coconuts, trees and other debris the cyclone would likely send flying.

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The storm has strengthened since hitting Samoa and American Samoa last week, where it caused damage to buildings, widespread power outages and flooding.

A supplied image shows locals covering windows to office buildings as part of preparations for Cyclone Gita in the Tonga capital of Nuku'alofa, February 12, 2018. Taniela Hoponoa/CARE Australia/Reuters

President Trump on Sunday declared an emergency in American Samoa, a U.S. territory. The declaration allows the Federal Emergency Management Agency to provide equipment and resources to help the 50,000 residents recover.

Tongan authorities said every family should have an emergency kit and those in flood-prone areas should move into evacuation centers. Authorities were urging others to keep of the roads and stay indoors.

Chris Brandolino, a scientist at New Zealand's National Institute of Water and Atmospheric Research, said the eye of the cyclone was expected to travel just south of the capital but could directly hit it. He said the cyclone was relatively compact, which means its path of destruction should be narrow.

Brandolino said flooding and coastal inundation would likely cause as many problems as the damage from the winds. He said that after hitting Tonga, the cyclone was forecast to travel west before slowly dissipating.

New Zealand Prime Minister Jacinda Ardern said her government was on standby and ready to help Tonga, which is home to about 105,000 people.

Aid agency Care Australia said it was also ready to assist. "With a storm this big, we have to prepare for the worst," said emergency response manager Stefan Knollmayer.