Tonga's northern island groups of Vava'u and Ha'apai are preparing for the arrival of hurricane-force winds with disaster agencies on standby for a response to Severe Tropical Cyclone Ian.
According to the most from the Fiji Meteorological Service, released at 5:00am local time (4:00am AEDT), Ian was located about 75 kilometres west of Vava'u and 140 kilometres north-northwest of Ha'apai.
It says the cyclone is currently moving south-southeast at 14 kilometres an hour.
Winds at the storm's centre are estimated to be averaging just over 200 kilometres an hour, with gusts of up to 290 kilometres an hour.
On its , Ian is expected to be about 140 kilometres south-southwest of Vava'u and about 18 kilometres southeast of Ha'apai at 0400 Saturday UTC time (5pm Saturday Tonga local time/3pm Saturday AEST).
Sanjay Prakash from the Fiji Meteorological Service told Australia Network the cyclone intensified.
"It has not changed its course, it is heading towards the Vava'u group in the northern part of Tonga," he said.
Mr Prakash says Ian is expected to hit Vava'u at around 9am local time Saturday (2000 Friday UTC/7am AEST).
He says Cyclone Ian will still be at least a Category 4, but possibly still a Category 5 system, when it reaches Vava'u.
"Once it heads towards Vava'u it will be maintaining possibly a southeast track, and accelerate," he said.
"Possibly the speed will increase and it is expected to move away from the Tongan group from eleven - midnight or eleven."
Very destructive hurricane-force winds from the storm are beginning to impact the islands.
Hotel manager, Kjell Stave, is bunkered down with his wife, child and six guests on Vava'u.
He's told Radio Australia they can already feel the force of the storm.
"The wind must be up to between 40 and 50 knots now," he said.
"But it's just the start of it I'm afraid.
Mr Stave says his power has gone out.
"I can see some boats fetching and rolling about here," he said.
"It's starting to build up some chop in the bay, we are fine, but we will have to see now."
Target of the storm
Fiji-based climate analyst Neville Koop says the Vava'u group of islands are at greatest risk.
"It is moving south east on a path that will take the centre of the cyclone very close to Vava'u in the early hours of tomorrow morning," he said.
"This is certainly capable of doing enormous levels of destruction and we hope that people there are secure because this is the sort of cyclone that could also lead to loss of life."
The capital, Nuku'alofa, is not directly in Ian's path but will experience damaging gale-force winds, heavy rains and sea flooding of low-lying areas.
The director of Tonga's National Emergency Management Office, Leveni Aho, says residents should prepare for the worst.
Mr Aho is urging affected residents to make sure they are well prepared.
"A reminder to people to make sure that they have enough supplies for the next 72 hours in terms of water, drinking water, and food and (ensure) some basic necessities like radios and mobile phones are charged to maintain communication," he said.
"Make sure that they are in a safe place if ever the winds arrive, keeping away from low-lying areas and the coastal areas, make sure that they are in a safe house, sheltered."
Disaster agencies on alert
The Pacific office of the UN Office for the Coordination of Humanitarian Affairs says Tonga's National Emergency Operations Committee met Thursday to discuss preparedness activities.
The Tongan Red Cross Society has emergency response teams on standby and can access pre-positioned non-food items across five islands.
The New Zealand government has additional personnel at the High Commission to support assessment and response planning.
Military assets are also available for reconnaissance and logistical support if required.
The UN says many people are boarding up windows and have cut leaves from fruit-bearing trees to reduce crop damage.
People in Vava'u have been preparing for the cyclone since yesterday afternoon.
The island group has a population of between 10 to 12,000 people.
Many of them live in small shelters set-up after the last major cyclone tore through the region, and there are grave fears many of these homes will be ripped apart by Ian.
© ABC 2014
11:16 EDT Thick fog engulfed the Sydney Basin on Saturday morning dropping visibility as low as 100m in some suburbs.