The Tongan Ministry of Health says the country is experiencing a spike in suspected measles, with 400 cases recorded in Nuku'alofa last week.
A medical officer at Vaiola Hospital, Viliami Vao, says about 25 people were admitted to hospital because of the seriousness of their cases.
He says the other patients were sent home while awaiting blood test results to have their cases confirmed.
But there is some doubt as to whether the fever and rash symptoms being experienced is measles, with some saying a mosquito-borne virus being more likely.
Dr Vao says the hospital hasn't seen a spike like this before, and is unsure of its cause.
"The number for last week was 400 suspected cases of measles, so we are still not sure how we end this spike because it's quite a new situation. We're just hoping this is the peak and from next week we'll have fewer and fewer numbers."
Viliami Vao is calling on the public to be cautious when in crowds to avoid spreading the illness further.
