Melbourne has just been rocked by an earthquake, with residents reporting strong shudders, offices being evacuated and tremors being felt as far away as Sydney, Canberra and Tasmania.
Geoscience Australia initially said a magnitude 6.0 quake was recorded at 9.15am near the town of Mansfield, Victoria, but later downgraded its rating to magnitude 5.9.
The quake was 10km deep, according to Geoscience Australia.
Mansfield is a small town in the foothills of the Victorian Alps. It is approximately 180km north-east of Melbourne by road.
"Widespread felt reports. If you have building damage or require SES assistance, phone 132500 and please be patient as lines may be busy," it said. "There is no tsunami threat."
A second quake, understood to be an aftershock and registering a magnitude of 4.0, has taken place in the same location.
According to Geoscience Australia the first quake was at 9.15am local time, and the second one, magnitude-4.0, was at 9.33am.
Residents from as far away as Dubbo in NSW have reported tremors from the quake.
It was felt 190km away in Melbourne as well as in regional Victoria, Sydney, regional New South Wales, the ACT, Adelaide and Launceston in Tasmania.
Melbourne's Seismology Centre says the earthquake lasted about 20 seconds.
New Zealand's GeoNet tweeted: "This is the largest on land earthquake in Australia since 1997. Earthquakes in Australia are reasonably uncommon, being far from the active tectonic zones of the Australian plate (like the one we live on!)"
A seismologist has told ABC radio in Melbourne this morning that it's the biggest earthquake Victoria has experienced since European settlement and there will be aftershocks, potentially one magnitude lower.
Garry Gibson said the last time Victoria felt anything like this was in 2009 in June, when there was a 5.5 magnitude earthquake. Australia-wide, there was a bigger one, a magnitude 6.1, or 6.2 near Broome in WA.
Office and apartment blocks across Melbourne have been evacuated but there are so far no reports of any injuries.
Images from Chapel Street in Melbourne show bricks strewn across the road and footpath from what looks like a collapsing burger joint - believed to be due to quake damage.
Mark Holcombe, the mayor of Mansfield, which was the epicentre of the quake, said it was "really strong" and caught everybody off-guard.
"It came right out of leftfield. We don't have earthquakes, that I am aware of, none of the locals I spoke to this morning had that experience with earthquakes here before, so it is one right out of leftfield. It was just a really big crumble," he told ABC Breakfast.
"It was really strong. I was sitting down at work at my desk and I needed to run outside, it took me awhile to work out what it was.
"I have been in earthquakes overseas before and it seemed to go on longer than I have experienced before. The other thing that surprised me was how noisy it was. It was a real rumbling like a truck going past."
New Zealander Colin - who lives in Melbourne's Ferntree Gully - told Newstalk ZB's Kerre McIvor it felt like being back home in Christchurch.
"About 30 seconds it lasted. I didn't know whether to run outside or upstairs.
"I'm in a solid concrete house, so it really shook. It shook as much as I've felt in Christchurch."
Victorian Premier Daniel Andrews made the first official reaction to the earthquake, tweeting at 9.47am: "Yes, that was an earthquake."
Prime Minister Scott Morrison then fronted a press conference in Washington DC - where he is taking part in the Quad leaders summit - to reveal the "rare event" had so far led to no injuries.
"These are very rare events in Australia and I am sure people would have been disturbed by that, particularly in the most immediate area effected," he said.
"The agencies at a state government level are there responding, and the federal Government will provide the support that is necessary."
The shudders were felt by the ABC Breakfast newsroom in Melbourne, where reporters said it was "quite frightening".
Host Michael Rowlands said: "It was quite frightening. I think you would agree.
"We were chatting here in the studio after the show, after we threw to you in the mornings coverage. We were chatting away and all of a sudden the studio started shaking, not to shaking and a minor violently."
Australia's Sky News is reporting damage to some buildings in Melbourne, along with vision of people milling in the streets of the CBD as offices are evacuated for safety precaution reasons.
More to come