A shallow magnitude 4.4 earthquake hit Victoria at 11.32am, and was felt in Melbourne's CBD and the southeastern suburbs.
A second, smaller quake - measuring 3.3 - shook the South Gippsland town of Korumburra, with reports it was again felt in Melbourne, at 12.37pm, a spokesman from Geosciences Australia said.
The epicentre of the original quake was about 7km west of Korumburra.
Later, a powerful earthquake struck New Zealand's North Island. The epicentre was about 72km southwest of Rotorua, and was felt as far south as Christchurch, but there were no reports of injuries or damage.
GNS Science in New Zealand said the earthquake - which struck at 1.36pm AEST - had a magnitude of 6.5, but the US Geological Survey measured the quake at 5.3.
Senior seismologist Clive Collins told Victorians they may feel further aftershocks today, and while it was unlikely the state would ever cop anything stronger, it should never be ruled out.
"If you look at the history of recorded earthquakes in Australia, they are not increasing or decreasing necessarily, it's just the luck of the draw," he said.
"But you can have clusters of activity within the space of a year and then nothing for five years.
"People are also hearing about it a lot more because they can just jump onto the internet.''
A number of tremors measuring between 1.8 and 4.6 originated near Korumburra in March and May 2009, with the largest on March 18 felt as far away as Bacchus Marsh, 50km west of Melbourne.
Mr Collins said the latest quake was probably part of the same fault line.
"Australia sits on the tectonic plate that runs from New Zealand to the Himalayas and we are not near any big boundaries but because the plates are moving all the time stresses can build up in local fault lines or cracks. That's what we've felt today.''
Korumburra Hotel publican Troy Patterson said when the earthquake hit, the pub shook for about eight seconds, accompanied by a loud rumbling. "The whole place literally shook,'' he told AAP. "You would think a truck had driven through the pub.''
Kara from Rowville, in Melbourne's southeast, said she initially thought it was the wind rattling the windows. "The windows rattled really loudly at first. I just thought it was the wind as it's really windy here,'' she told Fairfax Radio Network. "Then the couch I was sitting on started shaking. It felt like I was sitting on wobbly jelly or on the sea,'' she said.
Liz, from Monbulk, said it was the strongest earthquake she had felt. "The house really rattled for about 12 to 15 seconds,'' she said.
State Emergency Service spokesman Lachlan Quick said no reports of damage had been received so far.
The Geosciences Australia spokesman said the centre had received more than 300 reports from people who felt the quake. Most reports were of windows and crockery rattling, he said. Michael O'Keefe was in Warragul and said it was the strongest quake he's ever felt. "It sounded like a truck was approaching up the street and then it was as if the truck had run into the building. Everything was rattling. It feels a bit like it's not complete, like there is another one to come.''
Glenn Robins in Mt Waverly said he was sitting in his armchair when the tremor struck. "I felt it through the chair and then saw all the photos on the TV unit rattling.'' No major damage has been reported but reports of the quake have been received from the CBD as far north as Melbourne airport and east to Kilsyth and Lilydale.
Residents in Tullamarine, Baccus Marsh, the CBD, Croydon, Berwick, Ferntree Gully and Blackburn reported tremors. Steve at Lynbrook told his local Leader newspaper he thought the noise was coming from a nearby railway station. “Not sure if a truck just dropped a load at the nearby Lynbrook rail station construction site or we just has an earth tremor… the ground shook for about 30 seconds,’’ he said.
Andrea in Gembrook said the quake wasn’t as bad as the last tremor to shake her house. “I am in Gembrook and the house shook, bottles rattled and the animals were worried. not as big as the last one that cracked our wall,” she said.
Senior seismologist Clive Collins told Victorians they may feel further aftershocks today, and while it was unlikely the state would ever cop anything stronger, it should never be ruled out. "If you look at the history of recorded earthquakes in Australia, they are not increasing or decreasing necessarily, it's just the luck of the draw," he said. "But you can have clusters of activity within the space of a year and then nothing for five years. "People are also hearing about it a lot more because they can just jump onto the internet.''