A magnitude-3.9 earthquake has hit homes in Appin and surrounding suburbs, south of Sydney, just after 1:00am.

GeoScience Australia reported that the earthquake could have been felt in a 56-kilometre radius, which includes Wollongong, parts of the southern highlands and most of southern and western Sydney.

GeoScience seismologist Jonathan Bathgate said there had been more than 100 online reports and a number of calls from residents.

"Most people are not reporting any damage at this stage, but certainly are reporting shaking enough to have woken them up and knock objects off shelves, loose objects, and rattle windows and things like that," he said.

"So a magnitude-3.9 — it's certainly a good shake."

'Violent jolt' and 'loud bang': witnesses

Rebecca O'Neill who lives in Bulli, a northern suburb of Wollongong, felt the tremor about 1:20am.

"I was on the couch with my son and all of a sudden there was quite [a] violent jolt and shaking," she said.

The quake continued to rattle her windows for about a minute after the jolt.

"It did manage to shake my entire lounge room," she said.

"I think the jolt was so significant that if we would have been sleeping, it would have woken us — it set the dogs off."

Maria Furina lives in Menangle Park, a rural Sydney suburb near Campbelltown, about 20 kilometres north west of Appin.

"It was quite scary. We were woken up with a loud bang and then the bedroom windows started shaking and the sliding doors started shaking," Ms Furina said.

"And then I looked over to my child's cot and his mobile was shaking, and it woke the baby up as well.

"I actually froze and my partner jumped up and said 'there's been an earthquake', and I just didn't know what happened, I was quite stunned.

"It really shook us up. The horses were neighing in the paddock and running around, and the dogs were barking.

"I've lived in Menangle Park my whole life. I'm 29 now and that was definitely the strongest one I've felt, by far."

Area has a history of earthquakes

Since 1999, there have been earthquakes in the area ranging from magnitude-1.9 to magnitude-4.8.

The quakes generally occur every year or two, Mr Bathgate said.

"But it's not always consistent — in 2013 there were about five earthquakes in the space of a couple of months — so it certainly is an area that does have a history of seismicity."