Power has been restored to thousands of properties in Muswellbrook after a magnitude-4.1 earthquake shook the New South Wales Upper Hunter.
Geoscience Australia's monitoring website shows the quake's epicentre was near BHP's Mount Arthur mine site, south-west of Muswellbrook.
It was recorded at 12:12pm, with a revised depth of 3 kilometres.
It is the fourth earthquake larger than magnitude-4 since August.
Rod Hirst was in Muswellbrook as it hit and said he heard a bang and it shook the building.
"You felt the rock and the windows rattle but it wasn't as bad as the first one," he said.
"It didn't last long, only a couple of seconds."
Power supplier Ausgrid reported that more than 2,500 addresses lost power shortly after the quake with electricity restored around 2:30pm AEDT.
The ABC understands no injuries or damage have been reported at the BHP mine.
Quake swarm
The Upper Hunter has experienced more than 50 earthquakes since a major 4.7-magnitude quake shook the region on August 23, which was felt as far away as Coffs Harbour, Sydney, and Canberra.
Senior seismologist Hadi Ghasemi from GeoScience Australia labelled the ongoing activity an "earthquake swarm".
"In earthquake swarms, you have a series of earthquakes with similar size magnitudes — it's not like an aftershock sequence," Dr Ghasemi said.
"In this region, since the magnitude-4.7 in August, we've recorded over 50 earthquakes, four of them with magnitudes larger than 4, including the recent one."
The August 23 quake brought down brick chimneys and damaged homes and businesses.
Dr Ghasemi warned there may be more tremors to come.
"All of the previous magnitude-4 ones in this region were followed by smaller aftershocks," he said.
"But then again, with warm activity, this kind of activity may continue for months or even years to come."
BHP had notified Muswellbrook Shire Council it would be conducting a blast at the Mount Arthur Site today from 11am.
Dr Ghasemi said determining the cause of today's quake was "very difficult".
"There are certain studies indicating that the seismicity can be linked to the mining activity because whatever activity you are doing it could basically reduce the stress regime of the region itself and that may trigger earthquakes," he said.
"But at the same time, the mines are naturally located closer to fault lines because that's where the mineral deposits form."
Locals shocked
Concreter Mitchell Rando was on a worksite when the quake struck.
He said the wet concrete he had poured started to wobble when the earthquake struck.
"You could hear the fences shudder and feel the ground movement," he said.
Muswellbrook concreter Mitchell Rando said the quake almost ruined his work. (ABC Upper Hunter: Courtney Yeandle)
Bradley Brennan uses a wheelchair and said the earthquake left him rattled.
"It was shaking my wheelchair pretty well," he said.
Carron Henson was with Mr Brennan on Muswellbrook's main street at the time.
"I was scared, but it was smaller than the last one," she said.
"The last earthquake I actually got shook out of bed."