Research from the University of Newcastle and the Bureau of Meteorology has modelled the effects of tsunami inundation in Sydney and forecast the impact of the smallest and largest tsunamis on the harbour.

Lead report author Kaya Wilson said the research was about creating community awareness and making sure people took tsunami warnings seriously.

"It is something that could happen here and could be devastating ... We don't want people to worry, but we want them to be aware it is a very real threat," Mr Wilson told AAP.

"We want people to be aware of it as a hazard because it could be extremely dangerous."

There are two subduction zones closest to Sydney, one being near Vanuatu and the other south of New Zealand, where two tectonic plates meet under the ocean.

If an earthquake was to occur at either one of the zones and created enough tension, the force could push the water and cause a tsunami that could travel the distance to the east coast of Australia, Mr Wilson said.

While the likelihood of a major tsunami impacting NSW is low, if it did happen, the "Hollywood" style wall of water isn't what people would see, he added.

"If it's a really large earthquake it would be a sequence of waves not just one and there would be very quick rising and falling of the water levels," he said.

"It's like the whole ocean is moving up and down."

There is a risk a large tsunami could come onto land with the study finding Manly Corso and southern bays of the harbour such as Rushcutters Bay and Double Bay at most risk.

The waves could come on and off land at fast speeds lasting for hours and even days, Mr Wilson said.

The research found there's a risk of dangerous whirlpools forming near the Spit Bridge in Sydney's northern beaches which is reported to have happened in 1960 during the Chilean tsunami.

Project lead and coastal geoscientist Hannah Power said she wouldn't expect a risk to Sydney's CBD but strong currents and unpredictable rapid water movements would make the harbour an unsafe place to be.

"If you think about a two-metre swell, we wouldn't feel the need for concern, however a two-metre tsunami would be devastating," Dr Power said in a statement.

Australian Associated Press