SUVA, Feb. 12 (Xinhua) -- Tonga declared on Monday a state of emergency as the South Pacific island state prepares for severe tropical cyclone Gita that threatens to hit southern Tonga with a potential Category 5 force from Monday night.

According to Matangi Tonga online, the island state's leading news website, Tonga's Acting Prime Minister Semisi Sika declared the state of emergency due to the expected destructive winds and sea level rise.

Tonga has a population of over 100,000.

"We want to emphasize to the people the severity of this tropical cyclone and not take it lightly. The authorities are concerned about people's safety and it is important that they now prepare and make efforts to protect themselves and their properties," said Poasi Tei, Tonga's minister of meteorology, energy, information, disaster management, climate change and communications.

Under the state of emergency, a curfew in the central business district area of the capital city of Nuku'alofa will start from 9:00 p.m. local time Monday until 7:00 a.m. local time on Tuesday, Commissioner of Tonga Police Stephen Caldwell said on Monday night.

Acting Chief Executive Officer (CEO) for Tonga's Ministry of Internal Affairs Onetoto Anisi said they have called on district and town officers to ensure people who needed to be taken to evacuation centers to move on Monday because of the severity and danger of tropical cyclone Gita.

"It is vital that they are moved to buildings that can withstand a category 5 cyclone and ensure there is enough food, drinking water and there are first aid kits and records of people."

Tonga's Director of Meteorology 'Ofa Fa'anunu said a category 5 tropical cyclone will bring winds that have reached 110 knots or around 220-230 km per hour.

Truckloads of soldiers were moving around Nuku'alofa helping with storm preparations.

NASA's satellite images from space show the massive size of the storm, with the first clouds starting to brush Tonga after noon on Monday.

Gita has already caused serious damage in both Samoa and American Samoa.