© Le resau sismologique de Noevelle-CaledonieThe earthquake struck about 1:00pm local time.
The earthquake happened about 1:00pm (WST).
Walls were cracked at two homesteads in the Lake Muir region, but there were no other initial reports of damage.
The Bureau of Meteorology WA said there was no tsunami risk to Australia. It said the quake was centred near Lake Muir and forecasters working in its West Perth headquarters felt the building sway.
Senior Geoscience Australia seismologist Phil Cummins said it was the second earthquake to hit the region in a week.
"It occurred roughly between Walpole and Kojonup on the south coast, it was felt all the way from Albany up to Perth," he said.
"It is quite a large earthquake, it is large enough to cause damage but it's unlikely to have done so because it occurred in a relatively remote area."
Mr Cummins said the earthquake was uncommonly large.
"You would expect to get a 5.6 (magnitude) maybe once every couple of years throughout Australia," he said.
He said a magnitude-3.5 earthquake struck off the coast of Albany on Wednesday, while another magnitude-3.4 earthquake hit Walpole on Thursday.
A magnitude-4.3 earthquake struck Norseman in WA's Goldfields region last month.
'Like a bomb went off'
Mark Muir said he was having lunch at his home in Mordalup, close to the epicentre, when everything began violently shaking.
"It really felt like a bomb went off under your feet. It just kept on echoing through the ground for nearly 40 seconds, maybe up to a minute," he said.
Mr Muir said the noise was "like a huge underground explosion", and he still felt shaken two hours after the event.
"Everyone is safe and well but just a few of the old homesteads around here suffered a bit of damage with a few cracks in the wall, but nothing severe," he said.
Dardanup resident Jill Cross said she was watching TV when she felt her house shaking.
"I thought: 'am I having a bit of a giddy turn or something?'," she said.
"The ceiling fans and the light fittings were all swaying. It only lasted for a second or so but enough where you felt 'what's going on here?'."
Visitors and staff at Walpole's Tree Top Walk said they did not feel the quake but were rattled by a loud noise.
© Department of Parks and WildlifePeople at Walpole's Tree Top Walk experienced the earthquake as a loud noise.
"It sounded very heavy-duty, I also thought it could have been a truck coming past on the highway," she said.
"We had some tourists picnicking in the carpark and they said they saw the forest branches moving a lot.
Glynne Jones was at home in Northcliffe, about 70 kilometres from the epicentre, when he felt a heavy jolt.
"The whole house shook. It only lasted a couple of seconds, I didn't know if it was a truck going past so I rang a couple of other people and everyone felt it," he said.
Mr Jones said the last earthquake he experienced in Western Australia was a magnitude-6.9 earthquake in Meckering in 1968.
Twenty people were injured in that earthquake which also destroyed the town and left hundreds of families homeless.
Rocky Gully pub rattled
Helen Andrews, who runs the Rocky Gully Pub about 40 kilometres from the earthquake's epicentre, said she felt the whole building shake.
"I was in the kitchen preparing a meal and the whole place just started to rumble, it was a really deep heavy rumble, not like side to side shaking," she said.
"I thought someone might have been parking a really big heavy loud rumbling truck up in the parking area.
"I raced outside to see if something was on the roof. I just didn't know what was going on.
"I was starting to panic thinking maybe my big hot water system was blowing up."
However, she said nothing had been broken and she had not heard any reports of damage from customers.
The Australian Seismometers in Schools program, which has placed earthquake-measuring seismometers in schools across Australia, tweeted that the tremor had been recorded on several of its devices.
Mr Cummins urged people to register their experiences by filling out a Felt Report on Geoscience Australia's website.
"It gives us really important information about the level of shaking caused by this earthquake," he said.
"We know we can measure the intensity with instruments but for the shaking intensity we often rely on those felt reports."
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