The earthquake measuring 8.1 on the Richter scale hit near Macquarie Island in the Southern Ocean, more than 800 km (500 miles) southeast of Tasmania, at about 2 a.m. (1500 GMT), said Geoscience Australia seismologist Cvetan Sinadinovski.

"Usually this kind of earthquake happens every three to four years in the world, it is just a part of the dynamic cycle of the earth," Sinadinovski told Reuters.

The earthquake could have caused a tsunami, but no noticeable changes in water levels had been reported in Tasmania or New Zealand, Sinadinovski said. An aftershock measuring 6.1 hit at 6.50 a.m., he said.

"The last earthquake of similar magnitude in the Macquarie Rise region was in 1924. The magnitude of that earthquake was 7.5," Sinadinovski said.

It is the largest earthquake to hit since more than 120 people were killed in Peru when an earthquake measuring 8.4 on the Richter scale struck less than 200 km (125 miles) off the coast of the South American nation in June 2001.

The Richter scale measures the magnitude of an earthquake with a reading of more than 8 regarded as a "great" earthquake that can cause serious damage over several hundred kilometres and a reading of less than 2 considered micro.