Cyclone Pola is now a category two system and is continuing to strengthen.
The cyclone is fast moving as it heads south at 31km/h between Fiji and Tonga.
It is expected to pass between Tonga and Fiji within the next 48 hours, with Tonga likely to take most of the impact.
A gale force wind warning is in force for all of Tonga.
Tonga Metservice is warning people in the Niuas, Vava'u and Ha'apai that they will be the first to feel the effects of Cyclone Pola this afternoon.
Tongatapu and 'Eua should begin to experience more adverse weather conditions by this evening.
Cyclone Pola is continuing to strengthen and forecasters say there is a chance it could develop into a Category three system.
Fiji's Lau group of islands is the most likely to be affected by the cyclone on its current track.
RNZ Pacific will be broadcasting cyclone warnings via the Tonga MetService throughout the day.
People have been advised to monitor local radio broadcasts for the latest information.