Residents from around Adelaide have reported feeling an earthquake this morning, with one saying he heard a rumble when his pot plants started shaking.

Geoscience Australia has confirmed a quake — with preliminary magnitude of 4.9, an epicentre in waters south of Adelaide and a depth of about 10 kilometres — struck about 7:50am.

Callers to 891 ABC Adelaide reported rattling and shaking this morning for several seconds.

"I just made a cup of coffee and hopped back into bed and then the whole bed moved and my coffee spilt," Kate from Reynella in Adelaide's south said.

Brian from Goolwa said he noticed all the pot plants started vibrating and "heard a bit of a rumble".

Josh said he was at Mount Barker when he noticed windows rattling and "the dog went a bit crazy".

"[It] went [for] about three seconds. Definitely an earthquake, I think," he said.

In the first hour after the quake, Geoscience Australia's website listed about 700 "felt reports" from around Adelaide and as far as Kingston SE.

Geoscience Australia senior seismologist Jonathan Bathgate said the quake struck about 100 kilometres offshore, between Kangaroo Island and the south-east coast.

"It's a significant earthquake and that's reflected in the distance that the earthquake was felt," he said. 

"So we're getting 'felt reports' in from as far away as Gawler, all the way through the city, Kangaroo Island and all the way down to Beachport, so [it was] widely felt across the region.

"There is potential for aftershocks, for sure, from an earthquake of this size."

The quake comes just over a week after another, of magnitude-2.8, woke Barossa Valley residents in the middle of the night.

There have also been noticeable quakes in Victoria in the last few weeks.

'Four shakes from side to side'

Mr Bathgate said the latest quake was the consequence of tectonic movement associated with the Australian continent moving north by a rate of about 7 centimetres per year, but that it was unlikely to trigger any tsunami risk.

"This is probably way too small to trigger something like that," he said.

"Earthquakes offshore are always a concern that they could generate a tsunami, but generally they have to be significantly larger than this one."

Annie from the inner Adelaide suburb of Glenside told 891 ABC Adelaide she was in her apartment when she noticed shaking.

"I'm just sitting at the table, I'm on the third floor of a multi-storey apartment, and it just moved from north to south for about four shakes from side to side," she said.

"Obviously I didn't hear anything because it's all double glazed, but I heard the flex thing in the walls."

Willunga resident Mark said he did not hear anything, but "the house just started shaking crazily".

"It's not real stable and vibrates when the washing machine's spinning, but I got up to check that wasn't on," he said.

"I was sitting at the breakfast table and the next minute the wood started to shake," Goolwa resident Heather said.

"It was like several motorbikes starting up at once and everything, the ground, shook. Really moved," another resident, from nearby Hindmarsh Island, said.

In the state's south-east, the quake was reported around Cape Jaffa, Blackford and as far inland as Naracoorte and Hynam.

Cape Jaffa resident Mark Ireland said he was eating breakfast when the floor started to rumble and glasses on the table started to shake.

"I literally just thought it was some big heavy machinery going past, but it was probably a little more intense than that," he said.

"My wife and I looked at each other and said, 'Is that an earthquake?'

"There was no damage but definitely some rattling on the benchtops, glasses and things like that."

Mr Bathgate said there was a history of offshore earthquakes in the area, including a magnitude-5.6 earthquake offshore of Robe in 1948.

"That was quite a damaging earthquake. It was a lot closer to shore," he said.

He said Australia only got about five or six magnitude-5 quakes every year and more than 100 magnitude-3s.