WELLINGTON/SYDNEY (Reuters) - The Pacific nation of Tonga braced for destructive winds and potential flash flooding from Tropical Cyclone Gita on Monday after the powerful storm pummelled Samoa over the weekend.

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/Handout via REUTERS

The Category 4 storm was moving south across the Pacific and was expected to hit Tonga’s capital, Nuku’alofa, by 7 p.m. on Monday (0600 GMT), prompting the island nation to declare a state of emergency.

“Very destructive hurricane force winds are expected from this evening,” the Tongan Metservice said in a hurricane warning.

The Metservice said it expects Cyclone Gita to peak at a Category 4 event, but other regional meteorological agencies said the storm would reach Category 5, the most destructive wind-speed ranking.

Aid agencies warned of potential damage from heavy rain and winds, which the Metservice said could reach up to to 185 km per hour (115 mph).

Schools and workplaces in Tonga, which has a population of over just over 100,000, were closed ahead of the storm.

The Red Cross said residents were racing to identify strong buildings to be used for evacuations and to clean up debris such as loose wood or metal that could turn into dangerous missiles in powerful winds.

“That’s an incredibly strong cyclone ... people are getting prepared ... it really does save lives,” said Hanna Butler, Red Cross Pacific spokeswoman based in Fiji.

The Metservice also warned of huge coastal swells and flooding of low-lying areas.

Cyclone Gita pummelled Samoa and American Samoa, about 900 km (560 miles) to the northeast, over the weekend, flooding the Samoan capital, Apia. About 300 people had evacuated but were now returning to their homes, Butler said. Many people remained without clean, running water.

U.S. President Donald Trump declared emergency status for American Samoa, authorising the Department of Homeland Security and Federal Emergency Management Agency to coordinate disaster relief efforts.