A tsunami triggered by a major earthquake in New Zealand's south could reach Sydney in two hours and cause harbour currents to reach speeds up to eight metres a second, according to new modelling to be published on Tuesday.

Any tsunami that reaches Sydney is unlikely to have the walls of water seen in Hollywood films, but a large once-in-every 5000 year event would cause whirlpools in the Spit, flood Manly's Corso, damage jetties, boats and beaches, and trigger dangerous and powerful currents across the harbour, a new paper to be published in Nature's Scientific Reports on Tuesday concludes.

For the first time, coastal researchers from the University of Newcastle and the Bureau of Meteorology have modelled the effects of tsunami inundation in Sydney, using 3D mapping to show what would happen from the heads to inland at Parramatta.