More than 100 homes have lost roofs and at least 10 have been destroyed as Tropical Cyclone Winston lashes Tonga for a second time.
The storm is currently just north of the Northern Islands of Vava'u and is expected to make landfall early this afternoon.
Police and military are on standby in the country and residents are being told to stay indoors as the cyclone approaches.
Schools and some businesses have also closed in the country's capital Nuku'alofa.
Hundreds of people have already taken shelter in the 40 evacuation centres set up ahead of the storm's arrival.
The cyclone passed over the country earlier this week as a Category 2 storm, downing trees, powerlines and damaging buildings.
It has now been upgraded to Category 4 status, with winds gusting upto 250km/h.
Forecasters say it could become a Category 5 storm.
Popular tourist spot Vava'u and the Ha'apai islands are most at risk but predicting exactly where the cyclone will strike is not easy.
"There are indications that it is getting stronger but we're also not quite sure where it will hit, and that's part of the difficulty," says Oxfam New Zealand's executive director Rachael Le Mesurier.
She says aid agencies in the country have been working for years preparing for cyclones such as Winston, so there are processes in place to deal with the damage.
"It's about making sure that we have the supplies in the right place and not waiting for the cyclone to come along, so there's a degree of preparedness that we have in Tonga right now but we're also not sure exactly how much of an impact is going to hit."
There are also fears that the storm could further spread the Zika virus, with aid workers expressing concerns Cyclone Winston could disrupt access to running drinking water and hygienic drainage systems or mosquito control measures such as nets.
"The difficult is just being able to access water and the mosquitos particularly really like clean fresh water, so when lids are blown off the water tanks that's exactly where they go," says Ms Le Mesurier.
"We're both needing to get fresh water that's not contaminated and also do our best in effect, the Ministry of Health making sure that they can, as much as possible, treat the available fresh water."