The drill will test if the sirens can be heard by people nearby and familiarise them with the sound of the system.
The Director of the National Disaster Management Office, Liveni 'Aho, has told Radio Australia's Pacific Beat program that it's part of an overall plan to improve Tonga's early warning systems.
"Previously we were only using warning through text message, through mobile phones and radio but this has had limited coverage so what we are doing now is placing these sirens strategically in the areas most vulnerable to tsunamis," he said.
"We will be looking at doing it for the whole nation, but for the meantime what we are addressing is the vulnerable areas."
The test will be held today between midday and 4pm.
Time to evacuate
Mr 'Aho says the new warning system will alert people immediately, giving them a greater opportunity to evacuate to safety.
"If a tsunami is generated from the Tonga trench, which is lying just some 200 to 300 kilometres from us, we have very little time to react," he said.
"The aim is to give as much time for the general public to do something before any wave arrives."
If a tsunami is generated in the ocean near the Tonga trench, it's estimated the wave would take 10 minutes to reach Tongatapu.
Mr 'Aho says the National Disaster Management Office is also working on an evacuation plan to identify safe zones for people to flee to.
"Some of these areas have very limited access," he said.
"So we're working with our partners in trying to identify those areas and assist in getting road access to those particular areas that we've found out would be safe."