A state of emergency has been declared in Tonga overnight as tropical Cyclone Ula nears.
A tropical cyclone warning remain in force for Vava'u, Ha'apai, Tongatapu and Eua, the Tonga Meteorological and Coast Radio Services says.
The category three cyclone is 85 kilometres northeast of Vava'u this morning.
Winds are estimated of gusting up to 150 km per hour near its centre. It is currently moving southwest at a speed of 20 km per hour.
Winds are expected to increase to destructive speeds with momentary gusts up to 200 km per hour for Vava'u, with heavy rain and thunderstorms forecast, and possible flash floods expected.
Low-lying areas are expected to be flooded, with "very high to phenomenal seas" developing a damaging swell tonight.
A similar forecast is set for Tongatapu, Eua and Haapai, with Niuafo'ou and Niuatoputapu let off with the lightest winds of up to 55 km per hour.
The cyclone is expected to reach Fiji's Lau group by tomorrow morning.
Oxfam say it's ready to respond to the aftermath of Cyclone Ula as it passes over Tonga tonight.
The non-government organisation has said today it stands ready to send emergency staff to Tonga to assess the situation on the ground.
"We have emergency supplies in Tonga ready in place, so once the urgent needs are assessed we are ready to help coordinate the supply of clean water and sanitation for those affected by the disaster," says Pacific humanitarian manager for Oxfam New Zealand Carlos Calderon.
Oxfam is liasing with its partner Tonga National Youth Congress (TNYC), who will also help.
Oxfam and TNYC operate virgin coconut oil and organics programmes throughout Tonga.